Tympani are large, deeply resonant drums. When you go to the symphony, you'll most likely hear tympani being played.
Tympani, which are also known as timpani, timps, or kettledrums, are made of drum heads stretched across big metal bowls. The shape of their copper bodies explains the "kettle." The word tympani itself comes from the Latin root tympanum, or "drum." The sound of tympani is probably more familiar than you realize — the noise they make can sound just like thunder.