Business Capability
What a business does, expressed stably and independently of how it currently does it or who is responsible.
"Claims Adjudication" is a capability. "The claims team using the mainframe" is an implementation, an organisation and a technology all bundled together, and all three will change while the capability does not.
The value of the abstraction is exactly that stability. A capability map gives a vocabulary that survives reorganisations and replatforming, which makes it the right thing to hang application portfolios, investment and ownership off. It also exposes duplication with unusual clarity: five systems implementing the same capability is visible on a map and invisible on an org chart.
Two failure modes. Maps decomposed to four or five levels become unmaintainable shelfware, and maps drawn to mirror the current org chart record the present rather than describing the business.