For jacket in computer programming, see jacket function or jacket routine .

A jacket is a light coat.

A flak jacket is a MILSPEC jacket used by troops in wartime conditions. They were supposed to protect the body from shrapnel from 'flak' (fliegerabwehrkanone - WWII German 88 mm anti-aircraft guns) much like body armor, but were extremely poor at this.

See also: dust jacket, water jacket