Originally a celebration of the sun for the vikings in Europe. When christianity showed its ugly face in Europe, the Vikings where converted, and to compensate for the loss of their day of celebration, they claimed Jesus was born on this day. In Denmark, a certain type of porridge is still a very common thing to eat as one of the things for dinner at the 24th. Also, in (northern europe at least) Europe, gifts are unwrapped in the evening of the 24th of December, usually somewhat after dinner.
Oh my, didn't christianity rape this aspect of our lives as well ?