Defensibility is the ability of a business to sustain competitive advantage over time. It encompasses moat categories (network effects, scale, brand, switching costs, regulatory, IP) plus operational excellence, execution velocity that compounds small advantages faster than they can be copied, and continued investment in the mechanisms that produce defensibility. The discipline is more dynamic than "moats" suggests because most advantages erode over time without continued effort. It is the operational sister of moats: moats are the structures; defensibility is the practice of maintaining and strengthening them.
The defensibility framework:
Structural defensibility (moats):