A cappella

A cappella [snip]; Italian for "in the manner of the chapel") music is group or solo singing without instrumental accompaniment, or a piece intended to be performed in this way. The term "a cappella" was originally intended to differentiate between Renaissance polyphony and Baroque concertato style. In the 19th century, a renewed interest in Renaissance polyphony coupled with an ignorance of the fact that vocal parts were often doubled by instrumentalists led to the term coming to mean unaccompanied vocal music.

https://en.wikipedia.org/wiki/A_cappella