A cappella means to sing without an accompaniment. It is short for alla cappella – Italian for "in the chapel" – which, in the 16th century, would have meant unaccompanied. A cappella music can be polyphonic, homophonic, or unison. It is the opposite of cantata, which is accompanied singing.
Over the years, the a cappella style has expanded into genres such as pop, doo-wop, and barbershop quartets. Many modern a cappella groups or artists use their voices, through the technique of beat-boxing, to add percussive elements to their songs.
A particularly distinctive form of a cappella is barbershop music. This is characterized by consonant four-part chords for every melody note in a predominantly homophonic texture. Each of the four parts has its own role: generally, the lead sings the melody, the tenor harmonizes above the melody, the bass sings the lowest harmonizing notes, and the baritone completes the chord, usually below the lead.