Choir (music)
Music composed for choirs, or choral music, usually has at least two distinct vocal lines or parts that create harmony with one another. Although four vocal ranges are typically specified, composers of choral music often write more than four vocal lines. If the music divides into more than four parts this subdivision is typically shown by repeating the initials of the four voice parts to show which singers should be assigned to these vocal lines, e.g. SSAATTBB (for music in eight parts: two soprano lines, two alto lines etc.). Young children’s choirs may be unison choirs (all singing the same line), but older children will sing in two (SS) or three (SSA) parts or more.