nonchalance
Calm, relaxed behavior that shows you are not worried.
Nonchalance is a calm, casual attitude that shows you're not worried or bothered by something that might make other people nervous or excited. Someone with nonchalance acts relaxed and unbothered, as if whatever's happening is no big deal.
Picture a student who studied thoroughly for a big test: while classmates fidget and whisper nervously before the exam, she sits nonchalantly, calmly reviewing her notes without any visible stress. Or imagine a basketball player who sinks a game-winning shot and then walks back down the court with complete nonchalance, as if hitting clutch shots is just routine.
True nonchalance isn't faking confidence or pretending not to care. It's genuine ease that comes from being prepared, experienced, or naturally unflappable.
You might act with nonchalance when meeting new people, giving a presentation you've practiced, or handling a situation you've dealt with many times before. Someone who's nonchalant about performing on stage has probably done it enough times that the butterflies are gone. The opposite is acting anxious, flustered, or overeager, showing everyone exactly how much pressure you feel.