O come, o come, Emmanuel,
And ransom captive Israel,
That mourns in lonely exile here,
Until the Son of God appear.
Rejoice! Rejoice! Emmanuel shall come to thee, O Israel!

Emmanuel means "God is with us".  Emmanuel is the foretold name of the Messiah in the Old Testament.


SONGS OF ADVENT AND CHRISTMAS:
         O Come, O Come, Emmanuel
Making Music Praying twice has a nice printable for children to color to remind them of the name Emmanuel.
http://www.makingmusicprayingtwice.com/kids-activities/advent-christmas-activities#Meaning of Emmanuel

Bible Study Planet explains the verses of the songs. (Adult reading level)
http://biblestudyplanet.com/o-come-o-come-emmanuel-bible-study/