The term PERCUSSION SET can be broken down into two words: PERCUSSION and SET. PERCUSSION is a type of musical instrument that is played by striking or shaking, and a SET is a group of objects. In this case, the term PERCUSSION SET refers to a group of PERCUSSION instruments. One of these instruments is the TIMPANI, which is a type of drum with a bowl-shaped body and a membrane stretched over the top. It is typically played with mallets and has seven letters in its name.