The term 'trio minus one' is a musical term that refers to a group of two musicians playing together. The two musicians are known as a DUET (4 letters) and a DUO (3 letters). A DUET is a musical composition for two performers, while a DUO is a musical performance by two people. Both duets and duos are smaller versions of a trio, which is a group of three musicians. Therefore, the term 'trio minus one' refers to a group of two musicians playing together instead of three.