To clap is to strike your hands together. After an awesome play, an audience will clap and maybe even stand up and hoot. A clap is also any loud or sharp noise or collision, like a clap of thunder.
After you see a performance, it's polite to clap — smack your hands together quickly and repeatedly. To clap also means to put something down quickly and with force, like if you clap a plate on a table. Any sharp, loud sound is a clap, like a clap caused by an explosion. Clapping two objects together quickly will cause a clap. All types of claps and clapping involve sharp movements and loud sounds.