- antiaircraft fire, especially as experienced by the crews of combat airplanes at which the fire is directed.
- criticism; hostile reaction; abuse: Such an unpopular decision is bound to draw a lot of flak from the press.
- anti-aircraft fire or artillery
- informal a great deal of adverse criticism
1938, from German Flak, condensed from Fliegerabwehrkanone, literally “pilot warding-off cannon.” Sense of “anti-aircraft fire” is 1940; metaphoric sense of “criticism” is c.1963 in American English.