Here is a blog post that explains the ancient tradition of the "O Antiphons" that cover Dec. 17-23.
If you'd like a more local treatment of it, too- you can reference THIS blog's posts from a previous year:
December 17: O Wisdom
December 18: O Lord
December 19: O Flower of Jesse's Stem
December 20: O Key of David
December 21: O Radiant Dawn
December 22: O King of All Nations
December 23: O Emmanuel
