Do you have a preferred definition? Does it depend the number of type of instruments, or the type of the music itself, and can vocal music be part of chamber music?
Chamber music is a form of classical music, written for a small group of instruments which traditionally could be accommodated in a palace chamber. Most broadly, it includes any art music that is performed by a small number of performers with one performer to a part. The word “chamber” signifies that the music can be performed in a small room, often in a private salon with an intimate atmosphere.