Validation
Validation asks whether a product does the right thing — does it actually meet the user's real needs, independent of what the written spec says. It's typically checked late in development, through user acceptance testing or beta programs, and is distinct from verification, which checks whether the product was built correctly against its stated requirements.
The classic shorthand for the difference: verification asks "did we build the product right," validation asks "did we build the right product." A team can build something that perfectly matches every documented requirement — fully verified — and still validate poorly, if the requirements themselves didn't capture what users actually needed.
This is why user acceptance testing exists as a distinct phase even after a feature passes every internal test — it's specifically a validation check, run by or on behalf of actual users, catching the gap between "matches the spec" and "solves the real problem." A spec that's wrong from the start can pass verification completely while still failing validation.
