Bug bash
A time-boxed, all-hands session where a group deliberately tries to break a feature by using it in unscripted ways, surfacing defects that structured test cases miss. Bug bashes trade systematic coverage for diversity of perspective: a dozen people poking at a build for an hour find the edge cases nobody thought to write a test for.
A bug bash concentrates many people on exploratory testing of a feature in a short window, deliberately trading depth for breadth and fresh eyes. Its value is social as much as technical: people who didn't build the feature use it in ways the authors never would, and shared time-boxed focus surfaces issues a lone tester or an automated suite would miss. It complements, rather than replaces, structured regression testing.