1. Referring to how choral or vocal music is performed without instrumental accompaniment: At the school music performance, the students sang a cappella.
2. Etymology: from Italian, literally, according to (the style of the) chapel.

Descriptive of vocal music lacking instrumental accompaniment: The newlyweds had an a cappella group sing at the reception following their church wedding.

A vocal production or performance with no instrumental accompaniment: The a cappella consisting of male and female singers, performed weekly in the local church.