A cappella
A cappella music was originally used in religious music, especially church music as well as anasheed and zemirot. Gregorian chant is an example of a cappella singing, as is the majority of secular vocal music from the Renaissance. The madrigal, up until its development in the early Baroque into an instrumentally-accompanied form, is also usually in a cappella form. Jewish and Christian music were originally a cappella,[citation needed] and this practice has continued in both of these religions as well as in Islam.

Q: In what era was most of the vocal music considered A cappella?
Renaissance