If you look on the set days for Major Feasts in the church calendar (the ones set in bold), the stretch of feasts from December 25 to December 28 is the longest. They are as follows:
December 25- Christmas Day (of course!)
December 26- St. Stephen, one of the first deacons of the church
December 27- St. John the Apostle and Evangelist (more about his role as Evangelist here)
December 28- The Holy Innocents
Whenever the First Sunday after Christmas occurs on December 26-28, the feasts on and after that Sunday get transposed to the following day.
You can learn more about the namesakes for these feasts by clicking the links above. Happy learning!