Crash
When an application unexpectedly stops working — segfault, uncaught exception, kernel panic, OOM kill. Distinct from "hang" (frozen but not terminated).
Crash reports: Apple Crash Reporter, Windows Error Reporting, Google Breakpad/Crashpad, Sentry, BugSnag. Symbolization (mapping stack pointers to function names) requires debug symbols. Soft crash: only one thread/feature, can recover. Hard crash: the whole process dies. Kernel panic (Linux/macOS), Blue Screen of Death (Windows), Sad Mac (vintage macOS) are OS-level crashes. Crash-only software is a design pattern: treat all shutdowns as crashes → better recovery testing.