In Italian, a cappella literally means in chapel style. That's because back in the day, instruments were forbidden in the church (they still are in many orthodox churches, synagogues and mosques). Therefore, all music had to be sung, and only sung.
These days, a cappella generally refers to a song, sacred or secular, that's performed without instrumental accompaniment. Far from the chants of Gregorian monks, or the motets of Ockeghem, or even the traditional 1940s barbershop quartet, a... READ ON