what is December 25 vis a vis Christmas

December  25  or a week before that date is  actually the an ancient roman pagan festival in honor of  DEITY SATURN , called SATURNALIA  or termed as Birth of the Unconquered Sun.
This week long festivities are coupled with gift giving, partying, carnival, and merry making.  This continued up to the 4th century as ROMAN  empire became under Christian rule.
It is a public holiday in all forms of work.  At this time , slaves were treated to a banquet normally enjoyed by their masters. Rampant overeating , heavy drinking  became a rule. Greeting cards were also sent to someone normally coupled with gifts.  There were also carrolling where some people go to house to house singing naked.

In the 4th century , Christians copied this saturnalia festival hoping to take pagans to became christians. Finally early Christians adopted this style and make this date as the birth of JESUS.
 Up to this time this pagan style of festivities are being celebrated by christians but to celebrate the birth of Jesus.