Flak refers to anti-aircraft fire, typically consisting of explosive shells designed to target and destroy enemy aircraft. The term originated during World War II, derived from the German word "Fliegerabwehrkanone," meaning "aircraft defense cannon." Flak can be deployed from ground-based artillery or ships and is characterized by its ability to create a barrage of explosions in the air. In addition to its military meaning, "flak" is also used informally to describe criticism or backlash. For example, a public figure might receive flak for a controversial statement or action. This usage highlights the negative responses people can face in various situations, including politics and media.