choir is a group of singers, who sing sometimes in unison,
sometimes in 4-part harmony. Generally, the highest harmony part is
soprano (when sung by women or girls) or treble (when sung by boys). The next
part is alto, still written on the treble clef. The next part is tenor, sung by
men and written on the bass clef in hymn books, but written on the treble clef
at one octave above true pitch for most other choral music. The deepest
part is the bass, which is always written in the bass clef.