A piano trio is a piece written for a piano and two other instruments, or an ensemble that plays such music. It is one of the most common forms of classical chamber music. The two other instruments are usually a violin and a cello, with the cello typically having a subordinate role. Among the other combinations are violin and viola, violin and horn, violin and clarinet, flute and cello, flute and bassoon, clarinet and bassoon, and oboe and bassoon.