What is cappella singing?

A cappella (Italian: [a kkaˈpːɛlla]; "in the manner of the chapel") is a form of singing in which the voices that produce the music, without the use of any musical instruments other than the human voice.

Historically, a cappella music has been defined in terms of liturgical performances, oratorios and similar music (usually sacred), in which the only performers are singers; however, the modern meaning also encompasses non-liturgical polyphonic secular music, such as madrigals, and modern popular genres, such as barbershop, gospel, close harmony and doo-wop.