Reading some three-part a cappella music, I see "TAG for Three-part voices" above the staff. Any idea what that might mean?
19 is the measure number. There are 27 measures total in the song, so this is the start of the last 8 measures. There's an alternate ending for two voices that has written above the staff: "TAG for Two-part voices".
UPDATE: Besides the posted answers below, see http://en.wikipedia.org/wiki/Tag_(barbershop_music).