Meaning of A CAPPELLA in English

A CAPPELLA

[adjective] [before noun], [adverb] [not gradable] [specialized] - sung by a group of people without the help of any musical instrumentsThe choir's poor ensemble is disastrously exposed in the a cappella passages.Barber-shop choirs sing a cappella.

Cambridge English vocab.      Кембриджский английский словарь.