O Antiphons refer to the seven antiphons or short sentences sung or recited preceding the Magnifcat during Vespers, evening prayers, of the Liturgy of the Hours (or the Divine Office). In the Roman Catholic church, they are part of the special preparation known as the Octave before Christmas, December 17-23. December 24th is Christmas Eve and Vespers for that evening are for the Christmas Vigil.
The O Antiphons are prophetic titles for the Messiah and refer to the prophecy of Isaiah of the coming of the Messiah, the soon-to-be-born King of Kings.
The Liturgy of the Hours are beautiful prayers, prayed by monks and religious and also by the laity. They are best prayed in a group. There seem to be different versions of the O Antiphon prayers but the following prayers are from the USCCB.org website.
December 17
O Wisdom of our God Most High,
guiding creation with power and love:
come to teach us the path of knowledge!
December 18
O Leader of the House of Israel,
giver of the Law to Moses on Sinai:
come to rescue us with your mighty power!
December 19
O Root of Jesse’s stem,
sign of God’s love for all his people:
come to save us without delay!
December 20
O Key of David,
opening the gates of God’s eternal Kingdom:
come and free the prisoners of darkness!
December 21
O Radiant Dawn,
splendor of eternal light, sun of justice:
come and shine on those who dwell in darkness and in the
shadow of death.
December 22
O King of all nations and keystone of the Church:
come and save man, whom you formed from the dust!
December 23
O Emmanuel, our King and Giver of Law:
come to save us, Lord our God!