To chicken out means to lose your nerve and back away from something you planned to do because you became too scared or anxious. When someone chickens out, they were ready to try something challenging or risky, but fear got the better of them at the last moment.

Picture a kid standing at the edge of the high diving board, ready to jump, but then climbing back down the ladder instead. That's chickening out. Or imagine a student who practiced a speech all week but then asks the teacher if they can skip their turn when the day arrives.

The phrase comes from the idea that chickens are timid, easily frightened animals. When you chicken out, you're letting fear control your decision rather than pushing through it. A friend might say, “Don't chicken out on me now!” when they need you to follow through on something you both planned.

Chickening out is different from making a wise choice not to do something dangerous or foolish. If you decide not to skateboard down a steep hill without a helmet, that's good judgment. But if you've been planning to try out for the school play and suddenly refuse to go to auditions because you're nervous, that's chickening out.