The term 'Quartet Minus One' refers to a musical ensemble consisting of three musicians, instead of the usual four. This type of ensemble is also known as a TRIO. A TRIO typically consists of a piano, a string instrument such as a violin or cello, and a wind instrument such as a flute or clarinet. The term 'Quartet Minus One' is often used to describe a jazz ensemble, which usually consists of a piano, bass, drums, and a saxophone or trumpet.