The third "great" canticle in Luke's gospel (2:14) records the song the angels sang at the birth of Jesus. However, it is sometimes not counted as a canticle because it was expanded in later liturgical use into the Gloria, a longer text that began with this verse and became a regular part of the daily Mass (see PHH 247 for the complete Gloria text). The Latin incipit of this text, "Gloria in excelsis Deo," is often used independently as a chorus of praise, as in the refrain of 347 and other Christmas carols.
Psalter Hymnal Handbook