While this is my first Christmas as an admitted atheist, that doesn't mean the holiday is any less special. I've known for decades that Christmas wasn't a Christian invention and that Jesus (if he even existed) wasn't born on Dec. 25 or anywhere near that date. I suppose the holiday does have a slightly different meaning for me these days, as my critical thinking has led me to research about the holiday.
For instance, long before Christianity even existed, the ancient Romans celebrated Mithra the sun god on Dec. 25 with a pair of festivals: Saturnalia and Juvenalia. These celebrations centered around the wealth of agriculture (Saturnalia) and children (Juvenalia, hence juveniles). Gifts were exchanged, food was eaten.
But once Christianity took hold of Rome, that's when the Christ Mass took center stage. But the leaders didn't want to let go of their festivals, so these celebrations coincided with religion.
It doesn't stop there, either, as Christmas utilizes pagan practices from other cultures, too, including the winter solstice. Cultures that celebrated the winter solstice (the marking of the longest day of winter is behind them and spring and harvest is on the way) were aplenty, as evergreen trees were decorated and celebrated as a symbol of hope, meaning the cold winter couldn't claim the tree or the people.
There's so much more history I could delve into, but that's not the point. Christmas is not a Christian invention, even if Christ is baked right into the name. It's a holiday that is an amalgamation of pagan rituals and other long-forgotten cultures. When someone says Christmas is a Christian holiday you can proudly tell them it's anything but.