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BXP

NYSE: BXP · USD

BXP (BXP) Economic Moat Analysis50

Competitive advantages, dated evidence and erosion risks.

Narrow economic moat

BXP has a narrow location-based advantage in premier gateway-market workplaces. Controlled properties and sites, substantial executed leasing, long lease terms and improving same-property occupancy support differentiation. Pricing power is mixed: revenue per square foot increased, but net effective renewal pricing is undisclosed and operating costs remain a constraint. Similar competing properties, sublease availability and uneven office demand limit durability. Reported market outperformance is an issuer assertion, partly supported by disclosed operating results.

Intangible assets

Control of desirable gateway-market properties and development sites supports differentiated workplace demand. Executed leases and improving occupancy provide operating support for this location-based advantage; undeveloped capacity represents potential rather than an already earning advantage.

Durability
Property control and approximately 9.9-year weighted-average terms on second-quarter 2026 executed leases support multiyear persistence. The evidence supports a limited advantage, without establishing permanent scarcity or premiums beyond lease expiration.
Competitors
Comparison not established
Erosion risks
Similar properties and client subleases provide alternatives. Hybrid work, possible employment changes and weak life-science demand can erode demand. Maintaining differentiation requires capital spending. Occupancy declined in 2025 before improving in 2026, and investment impairments demonstrate that asset quality does not prevent losses.
What would invalidate the thesis
The advantage would be undermined by sustained declines in comparable-property occupancy and revenue per square foot, failure to replace expiring leases, or evidence that concessions and tenant improvements eliminate rental premiums. Persistent underperformance against comparable local properties would directly contradict the differentiation claim.
Evidence (7) · Counterevidence (7)

Changes since the previous analysis

  • Retain the narrow verdict, now supported by 2026 executed leasing, demonstrated renewals and improving same-property occupancy.
  • Replace the previous nine-month 2025 operating comparison with full-year 2025 and first-half 2026 evidence. Revenue per square foot improved in both periods; occupancy fell in 2025 and recovered in 2026.
  • Remove the previous portfolio backlog through 2050 and approximately 7.9-year lease-term claims because those passages are absent from this catalog. Current executed second-quarter 2026 leases averaged approximately 9.9 years.
  • Retention now has direct renewal-volume evidence, although a renewal rate remains unavailable.
  • Reassess management from current disclosures: include completed 2026 dispositions and actual 2023 MYLTIP forfeitures. The 2025 OPP awards were granted, rather than merely proposed; their performance hurdles do not establish that awards were earned.
  • Retain governance grade 3 using disclosed independent committees, annual terms and related-person review policy; do not preserve the earlier nine-of-eleven independence claim, which is not established by the supplied passages.

Evidence limitations

  • Competition is disclosed through generic categories. No supplied entity is expressly established as a competitor; director affiliations, tenants and joint venture partners are not treated as competitors.
  • All sources are issuer filings. Claimed market outperformance and scarcity lack quantified comparable-property benchmarks, and premier workplaces is an issuer-defined classification.
  • Revenue per square foot is observed operating evidence, but does not isolate comparable-space renewal rents, contractual escalators, tenant mix or cash pricing after concessions and improvements.
  • Renewal volumes and lease terms establish demand and commitment, but do not establish a renewal rate, quantified relocation costs or dependence on BXP after expiration.
  • Executive ownership and ownership-guideline compliance are not established. Performance-linked awards and actual forfeitures support an alignment assessment without resolving the full pay-versus-performance relationship.
  • The supplied proxy establishes governance arrangements as disclosed on April 10, 2026, not subsequent shareholder voting outcomes. Source dates are filing dates, not retrieval dates.
  • Future development capacity, the asset-sale objective and anticipated benefits from reduced construction remain potential outcomes.

Financial indicators to test against the thesis

Calculated from annual filings. Missing data remains unavailable. Detailed financial charts remain in the other topics.

Financial indicators to test against the thesis
PeriodGross marginOperating marginROICFCF margin
202162.8%———
202262.1%———
202361.1%———
202459.9%———
202559.1%———

Pricing power50

  • Pricing outcomes

    Same-property revenue per square foot increased by approximately $1.70 in 2025 and $1.08 in first-half 2026. These observed outcomes support mixed pricing power alongside claimed market outperformance. Net effective renewal pricing after concessions and improvements is unavailable.

  • Customer demand

    Approximately 1.5 million square feet of second-generation renewals commenced in first-quarter 2026, providing direct repeat-demand evidence. Long newly executed leases and improved occupancy add support. No renewal rate is disclosed, and termination income increased.

  • Margin resilience

    First-half same-property lease revenue excluding termination income increased $36.8 million against $28.8 million of additional operating expenses, supporting operating-profit resilience. First-quarter expenses increased $18.8 million against only $12.4 million of additional lease revenue. Increased termination income is not treated as recurring pricing strength.

  • Pricing freedom

    BXP negotiates inception and subsequent rental rates, duration, allowances and concessions. Agreed multiyear terms limit immediate repricing, while similar properties and subleases constrain bargaining power. Potentially unfavorable renewal terms are disclosed risks rather than proven portfolio-wide outcomes.

Management56

  • Capital discipline

    Completed 2025 sales generated $682.5 million of net proceeds, followed by $225.3 million from the listed first-half 2026 joint venture sales. Completed financing and capital recycling support discipline, but substantial investment spending, $2.5 billion of estimated remaining development funding at year-end 2025 and repeated impairments temper the assessment. The $1.9 billion sale objective remains a plan; realized development returns are unavailable.

  • Incentive alignment

    Actual awards link compensation to multiyear TSR, FFO growth, leverage and stock-price hurdles. The completed 2023 MYLTIP period produced a 95% target payout and 168,717 forfeited units, demonstrating that conditions can reduce awards. Double-trigger provisions add support. Ownership compliance and the overall compensation-outcome relationship remain unestablished; granted OPP awards are not assumed earned.

  • Execution

    Executed leases, commenced renewals, improved 2026 same-property occupancy, completed asset sales and properties placed in service demonstrate delivery. Investment impairments, 2025 occupancy weakness and uneven demand offset those achievements. Leasing is evidence of commercial execution, not a client-satisfaction measurement; project returns and budget adherence are unavailable.

  • Governance

    Actual disclosures establish fully independent Audit, Compensation and NCG committees, annual director terms and annual independent review of ongoing related-person transactions. These support strong formal oversight. No tenure limits apply, subsequent voting outcomes are absent, and exceptional governance effectiveness is not demonstrated.

Sources and methodology

Current publication · Updated 19/10/2026 · Version 7

AI interpretation based on checked source excerpts. Issuer assertions and evidence limitations remain explicit.

Policy quality-scores-2: six equally weighted categories. The overall score requires full coverage. Missing inputs are not zero. Qualitative grades are sourced interpretations, not probabilities. 3/6 · 22/10/2026

Moat50

Equal-weight average of four evidence-backed rubric grades (0–4), scaled to 100.

structural advantage · 2/4 · Controlled gateway-market properties and sites, executed leasing and improving occupancy support location-based differentiation. Similar local alternatives and unquantified issuer-reported market premiums limit evidence of structural scarcity.

durability · 2/4 · Property control and approximately 9.9-year terms on executed second-quarter leases support multiyear persistence. Continued premiums at expiration are unproven. Reduced construction could help, but its future benefit is management's expectation.

customer dependency · 2/4 · Long executed lease terms and approximately 1.5 million square feet of commenced renewals demonstrate contractual commitment and repeat demand. They do not establish operational dependence, measured switching costs or lack of alternatives.

erosion resilience · 2/4 · First-half 2026 occupancy and revenue per square foot improved after 2025 occupancy declined. Weak life-science demand, recurring investment impairments and substantial maintenance and tenant spending temper resilience. Generic demand risks are treated as possibilities.

Pricing power50

Equal-weight average of four evidence-backed rubric grades (0–4), scaled to 100.

realized pricing · 2/4 · Same-property revenue per square foot increased by approximately $1.70 in 2025 and $1.08 in first-half 2026. These observed outcomes support mixed pricing power alongside claimed market outperformance. Net effective renewal pricing after concessions and improvements is unavailable.

retention · 2/4 · Approximately 1.5 million square feet of second-generation renewals commenced in first-quarter 2026, providing direct repeat-demand evidence. Long newly executed leases and improved occupancy add support. No renewal rate is disclosed, and termination income increased.

margin resilience · 2/4 · First-half same-property lease revenue excluding termination income increased $36.8 million against $28.8 million of additional operating expenses, supporting operating-profit resilience. First-quarter expenses increased $18.8 million against only $12.4 million of additional lease revenue. Increased termination income is not treated as recurring pricing strength.

contractual freedom · 2/4 · BXP negotiates inception and subsequent rental rates, duration, allowances and concessions. Agreed multiyear terms limit immediate repricing, while similar properties and subleases constrain bargaining power. Potentially unfavorable renewal terms are disclosed risks rather than proven portfolio-wide outcomes.

Predictability—

Missing exact annual revenue, free cash flow or FCF margin; operating cash flow and capex must both be reported for all five years.

Financial strength—

Missing required inputs: debtFcfGrade, netDebtEbitGrade, currentRatioGrade. Equal-weight grades: debt/FCF (1–8x), net debt/earnings before interest and tax (0–5x), interest service (1–12x), current ratio (0.75–2x). Earnings use reported operating income, or reported pretax profit plus reported interest expense when operating income is unavailable. Interest service uses earnings/interest expense; if unavailable, it uses reported operating cash flow/cash interest paid, without relabeling cash paid as accrued expense. Nonpositive cash flow/earnings score 0 for their service component; reported zero interest with a positive numerator scores 100. Net cash scores 100 for net leverage. Missing disclosures remain unavailable. General nonfinancial-company rubric, not a credit rating; exceptional and nonoperating gains are not normalized out. IFRS finance-cost and cash-flow classifications retain their reported scope.

interestCoverageGrade
7.63
cashInterestPaid
677.16
cashInterestCoverage
1.84

Capital allocation—

Missing required inputs: operatingReturn, cashConversionGrade. Three-year equal-weight indicators: pretax return on average invested capital (0–25%; equity + debt − cash, each year and its prior year), share-count growth (0–5%, lower better), share-based cost/revenue (2–20%, lower better), consolidated FCF/net income (0–1x). Return uses reported operating income or, if unavailable, EBIT calculated from reported pretax profit plus reported interest expense; exceptional/nonoperating gains are not normalized out. Share-based cost uses the reported cash-flow add-back or, if absent, separately reported recognized compensation expense; the latter never becomes an FCF adjustment. Nonpositive net income scores 0 for cash conversion; absent income/FCF stays unavailable. Nonpositive invested capital has no defined return and remains unavailable. Does not establish acquisition quality or buyback timing.

3-year average dilution (%)
0.34
3-year average SBC / revenue (%)
1.38

Management56

Equal-weight average of four evidence-backed rubric grades (0–4), scaled to 100.

capital discipline · 2/4 · Completed 2025 sales generated $682.5 million of net proceeds, followed by $225.3 million from the listed first-half 2026 joint venture sales. Completed financing and capital recycling support discipline, but substantial investment spending, $2.5 billion of estimated remaining development funding at year-end 2025 and repeated impairments temper the assessment. The $1.9 billion sale objective remains a plan; realized development returns are unavailable.

incentive alignment · 2/4 · Actual awards link compensation to multiyear TSR, FFO growth, leverage and stock-price hurdles. The completed 2023 MYLTIP period produced a 95% target payout and 168,717 forfeited units, demonstrating that conditions can reduce awards. Double-trigger provisions add support. Ownership compliance and the overall compensation-outcome relationship remain unestablished; granted OPP awards are not assumed earned.

execution · 2/4 · Executed leases, commenced renewals, improved 2026 same-property occupancy, completed asset sales and properties placed in service demonstrate delivery. Investment impairments, 2025 occupancy weakness and uneven demand offset those achievements. Leasing is evidence of commercial execution, not a client-satisfaction measurement; project returns and budget adherence are unavailable.

governance · 3/4 · Actual disclosures establish fully independent Audit, Compensation and NCG committees, annual director terms and annual independent review of ongoing related-person transactions. These support strong formal oversight. No tenure limits apply, subsequent voting outcomes are absent, and exceptional governance effectiveness is not demonstrated.

Evidence

At December 31, 2025, we owned or had joint venture interests in a portfolio of 179 commercial real estate properties, aggregating approximately 52.6 million net rentable square feet of primarily premier workplaces, including eight properties under construction/redevelopment totaling approximately 3.5 million net rentable square feet.

Business / portfolio ownership and joint venture interests · Filed 27/02/2026

•our control of sites in our markets that could support, as of December 31, 2025, approximately 13.6 million and 4.7 million of additional square feet of new office and residential developments, respectively; 7 Table of Contents •our reputation gained through 56 years of successful operations and the stability and strength of our existing portfolio of properties;

Business / controlled development sites and claimed reputation · Filed 27/02/2026

Over the past several years, BXP’s experience and performance has diverged from the larger market sentiment, as premier workplaces have outperformed the broader office market consistently and substantially in both rental rates achieved and occupancy.

MD&A / issuer-reported rental and occupancy outperformance · Filed 06/08/2026

Activity is increasingly concentrated in BXP’s premier office locations, including Midtown Manhattan, Boston's Back Bay, Reston Town Center, and select San Francisco submarkets, where tightening availability and improving demand are contributing to leasing momentum.

MD&A / leasing activity in premier locations · Filed 06/08/2026

In the second quarter of 2026, we executed 106 leases totaling approximately 1.8 million square feet with a weighted-average lease term of approximately 9.9 years.

MD&A / second-quarter 2026 executed leases and lease terms · Filed 06/08/2026

The increase was a result of our average revenue per square foot increasing by approximately $1.08, contributing approximately $19.5 million, and our average occupancy increasing from 88.1% to 89.1%, contributing approximately $17.3 million.

MD&A / first-half 2026 same-property revenue per square foot and occupancy · Filed 06/08/2026

Vacant space available at the beginning of the period 6,342,127 Vacant space from property dispositions/properties taken out of service (1) (389,363) Vacant space from properties placed (and partially placed) in-service (2) 30,284 Leases expiring or terminated during the period 2,190,499 Total space available for lease 8,173,547 1st generation leases (3) 120,757 2nd generation leases with new clients (4) 794,173 2nd generation lease renewals (4) 1,501,848 Total leases commenced during the period (5) 2,416,778 Vacant space available for lease at the end of the period 5,756,769 __________________ (1)Total square feet from property dispositions during the three months ended March 31, 2026 consists of 260,762 square feet at Gateway Commons and 79,382 square feet at North First Business Park.

MD&A / first-quarter 2026 commenced leases, renewals and vacancy reconciliation · Filed 07/05/2026

We face significant competition from developers, owners and managers of office, life sciences and residential properties and other commercial real estate, including sublease space available from our clients.

Risk factors / competing property owners and client sublease space · Filed 27/02/2026

Substantially all of our properties face competition from similar properties in the same market.

Risk factors / similar competing properties in the same markets · Filed 27/02/2026

•sustained changes in client preferences and space utilization from full-time, collective in-person work environments to hybrid or remote work models and/or changes from workforce reduction due to artificial intelligence, which could decrease overall demand for workplaces and negatively impact market rental rates and property values;

Summary of risk factors / hybrid work and potential employment changes · Filed 27/02/2026

Life science leasing demand remains below historical levels, particularly among earlier-stage 44 Table of Contents companies, and certain markets continue to experience a more measured pace of leasing activity.

MD&A / life-science leasing demand below historical levels · Filed 06/08/2026

The increase was a result of our average revenue per square foot increasing by approximately $1.70, contributing approximately $57.3 million, partially offset by approximately $13.8 million due to our average occupancy decreasing from 89.1% to 88.7%.

MD&A / 2025 same-property revenue per square foot and occupancy · Filed 27/02/2026

During the years ended December 31, 2025, 2024 and 2023, the Company recognized an other-than-temporary impairment loss on its investments in one, three and four joint ventures, respectively, totaling approximately $145.1 million, $341.3 million and $272.6 million, respectively.

Financial statement notes / joint venture impairments in 2023–2025 · Filed 27/02/2026

Cash used in investing activities for the year ended December 31, 2025 and December 31, 2024 is detailed below: Year ended December 31, 2025 2024 (in thousands) Acquisitions of real estate (1) $ (55,864) $ (35,366) Construction in progress (2) (683,750) (651,346) Building, pre-development and other capital improvements (3) (216,687) (189,667) Tenant improvements (338,808) (258,312) Proceeds from sales of real estate (4) 682,514 602 Acquisition of real estate upon consolidation of unconsolidated joint ventures (net of cash) (5) — 6,086 Capital contributions to unconsolidated joint ventures (6) (258,752) (132,096) Capital distributions from unconsolidated joint ventures (7) 172,662 28,325 Investment in non-real estate investments (3,538) (2,500) Issuance of note receivables (including related party) (8) (22,861) (3,258) Proceeds from note receivables (including related party) (8) 80,000 — Investments in securities, net 558 136 Net cash used in investing activities

Liquidity and capital resources / actual investing expenditures and proceeds · Filed 27/02/2026

When making leasing decisions, we consider, among other things, the creditworthiness of the client and the industry in which it conducts business, the length of the lease, the rental rate to be paid at inception and throughout the lease term, the amount of any security deposit or letter of credit posted by the client, the costs of tenant improvement allowances, free rent periods and other landlord concessions, anticipated operating expenses and real estate taxes, the date by which we expect to begin revenue recognition for the lease under GAAP, current and anticipated vacancy in our properties and the market overall (including sublease space), current and expected future demand for the space, the impact of other clients’ expansion rights and general economic factors.

MD&A / lease pricing, duration, allowances and concessions · Filed 06/08/2026

Lease revenue (excluding termination income) from the Same Property Portfolio increased by approximately $36.8 million for the six months ended June 30, 2026 compared to 2025.

MD&A / first-half 2026 same-property lease revenue excluding termination income · Filed 06/08/2026

Real Estate Operating Expenses Real estate operating expenses from the Same Property Portfolio increased by approximately $28.8 million, or 4.6%, for the six months ended June 30, 2026 compared to 2025.

MD&A / first-half 2026 same-property operating expense increase · Filed 06/08/2026

Real Estate Operating Expenses Real estate operating expenses from the Same Property Portfolio increased by approximately $18.8 million, or 6.0%, for the three months ended March 31, 2026 compared to 2025, primarily due to increases in (1) utilities and roads/grounds/security expenses of approximately $9.7 million, or 14.7%, and (2) real estate operating expenses of approximately $9.1 million, or 3.7%.

MD&A / first-quarter 2026 same-property operating expense increase · Filed 07/05/2026

Lease revenue (excluding termination income) from the Same Property Portfolio increased by approximately $12.4 million for the three months ended March 31, 2026 compared to 2025.

MD&A / first-quarter 2026 same-property lease revenue increase · Filed 07/05/2026

Termination income for the six months ended June 30, 2026 and 2025 related to 18 and three clients, respectively, across the Same Property Portfolio and totaled approximately $15.7 million and $0.8 million, respectively.

MD&A / first-half 2026 lease termination income · Filed 06/08/2026

Even if clients decide to renew or lease new 21 Table of Contents space, the terms of renewals or new leases, including the cost of required renovations or concessions to clients, may be less favorable to us than current lease terms.

Risk factors / renewal terms, renovations and concessions · Filed 27/02/2026

Dispositions and Impairments During the year ended December 31, 2025, excluding our unconsolidated joint ventures, we completed eight sales transactions for an aggregate gross sales price of approximately $702.6 million, resulting in net proceeds of approximately $682.5 million and gains on sales of real estate of $175.0 million and $177.6 million for BXP and BPLP, respectively (See Note 3 to the Consolidated Financial Statements).

Business / completed 2025 dispositions, proceeds and gains · Filed 27/02/2026

Dispositions The following table represents the Company’s share of the sales that occurred during the six months ended June 30, 2026 (dollars in thousands): Company’s share Property Ownership Sold Location Date Disposed Square Feet Gross Sale Price Net Cash Proceeds Gain on Sale Gateway Commons (1)(2) 50.00% South San Francisco, CA January 2, 2026 792,700 $ 150,000 $ 131,765 $ 6,719 7750 Wisconsin Avenue (3) 50.00% Bethesda/Chevy Chase, MD March 19, 2026 735,600 215,000 83,293 34,840 13150 Worldgate Drive (4) 50.00% Herndon, VA June 4, 2026 N/A 10,275 10,248 832 1,528,300 $ 375,275 $ 225,306 $ 42,391 _______________ (1)The Company had previously recognized an other-than-temporary impairment loss on its investment.

Financial statement notes / completed first-half 2026 joint venture dispositions · Filed 06/08/2026

We estimate our share of the aggregate estimated total investment to complete these projects is approximately $3.9 billion, of which approximately $2.5 billion remained to be invested as of December 31, 2025.

Business / estimated development investment and remaining funding · Filed 27/02/2026

•Issued $1.0 billion of 2.00% unsecured exchangeable senior notes due 2030 in September 2025.

Business / completed exchangeable senior note issuance · Filed 27/02/2026

We also partially or fully placed in-service four properties that totaled approximately 727,000 net rentable square feet (See Notes 3 and 6 to the Consolidated Financial Statements).

Business / properties partially or fully placed in service during 2025 · Filed 27/02/2026

BXP Three months ended March 31, Two of the components are each weighted 40% and utilize BXP’s TSR and BXP’s diluted Funds from Operations (“FFO”) per share growth, respectively, over a three-year measurement period as market condition and performance metrics, respectively, and the third component utilizes a leverage ratio as the performance metric.

Equity compensation / 2026 MYLTIP performance metrics · Filed 07/05/2026

The following table shows the results for the 2023 MYLTIP awards (after giving effect to employee separations) at the end of its respective three-year measurement period (Aggregate value is shown in millions): Measurement Date Final Payout as a % of Target Aggregate Value Forfeited Units 2023 MYLTIP Awards February 6, 2026 95 % $ 9.9 168,717 34 Table of Contents Issuances (Restricted Stock, LTIP Units and MYLTIP Units)

Equity compensation / completed 2023 MYLTIP measurement and forfeitures · Filed 07/05/2026

The OPP awards are 100% tied to rigorous dividend-adjusted stock price hurdles, with no units vesting unless our dividend-adjusted stock price reaches at least $90 per share for 20 consecutive trading days during the four-year performance period, while a +70% increase (as of the grant date) was required to earn the maximum number of units based on the $69.45 per share closing stock price on the grant date (see “—2025 Outperformance Awards” within this CD&A for more details of the award design).

Compensation discussion / granted 2025 OPP performance hurdles · Filed 10/04/2026

All time-based equity awards and the 2025 OPP awards include “double-trigger” vesting, meaning that if there is a “change of control” and the awards are not otherwise canceled in connection with the change of control transaction, then they only become fully vested if, within 24 months after the change of control, the executive’s employment is terminated by the Company or its successor without “cause” or the executive resigns for “good reason.”

Compensation policies / double-trigger vesting · Filed 10/04/2026

•the independent committees of our Board of Directors: each of the Audit Committee, Compensation Committee and NCG Committee is led by independent committee chairs and is comprised solely of independent directors; and

Corporate governance / actual independence of key committees · Filed 10/04/2026

Because each director is elected to hold office for a one-year term expiring at the next annual meeting of stockholders, and in light of the benefits resulting from continuity on the Board, the Board does not believe it is in the best of interests of the Company or its stockholders to establish arbitrary term limits or limits on the overall tenure of a director.

Corporate governance / annual director terms and absence of tenure limits · Filed 10/04/2026

In addition, any related person transaction previously approved by a majority of the independent directors of our Board or otherwise already existing that is ongoing in nature shall be reviewed by a majority of the independent directors of our Board annually to ensure that such related person transaction has been conducted in accordance with the previous approval granted by such independent directors, if any, and remains appropriate.

Related person transactions / annual independent director review policy · Filed 10/04/2026

We do not consider the expression “premier workplaces” a classification of our properties in accordance with any standard listing criteria in the real estate industry.

Business / nonstandard definition of premier workplaces · Filed 27/02/2026

However, a key component of our current strategic action plan introduced at our September 2025 Investor Day is the execution of a multi-year asset sales program to generate approximately $1.9 billion in net proceeds to fund our development pipeline and reduce leverage.

Dispositions / planned multiyear asset sales program · Filed 27/02/2026

On the supply side, new office construction has effectively slowed to a halt across most of our markets, which we expect will improve long‑term supply‑demand fundamentals and reinforce the relative competitiveness of institutional, well‑amenitized assets.

MD&A / issuer outlook for slowed construction and future supply-demand benefits · Filed 06/08/2026

Publication history

Publication history
VersionUpdatedCompetitive advantage
722/10/2026narrow
619/10/2026narrow
519/10/2026narrow
418/10/2026narrow
318/10/2026narrow
218/10/2026narrow
118/10/2026Unavailable

Sources

Research methodology and limitations · What is an economic moat?