A duet is a musical composition for two performers, most often used for a vocal or piano duet. For other instruments, the word Duo is often used.

The word duet is generally used in any of the following ways:

• a pair of musicians playing the same musical instrument,
• a pair of musicians playing different instruments,
• the performance of a song by two people,
• a piece of music that can be performed by two people,
• as a general term for any activity done by two people.

In Renaissance music, a duet specifically intended as a teaching tool, to be performed by teacher and student, was called a bicinium.