UXmas is run by the fine folks here at UXMastery.com, and it's sort of an UX-based advent calendar. Our fearless leaders (namely @HAWK, @natassja, and @Lukcha) ask a few community members and UX experts to submit some fun, loosely-UX-based content, to be published once a day over the 24 days before Christmas.
The 2016 edition had some great pieces. @HAWK wrote about The Laughs (And Fires) of Christmas Past, Steve Portigal wrote about flexibility in user research in his Semper Gumby piece, while Cameron Rogers and Scott Lacey gave us unforgettable UXmas at the House of Henry Ford comic.
So you get the idea. It could be videos, it could be comics, it could be articles, it could be... something else, I imagine, if someone were so inclined.
The team here recently sent out invitations to people to submit content for the 2017 version of the event, which generated the UXmas Topic Brainstorming thread.
If you weren't asked to submit some work, don't be too disappointed. There are, after all, only 24 spaces, and it would be impossible for the team here to include pieces from all of the great community members. If you're interested in writing or submitting content to the UXMastery site, I suggest getting in-touch with one of the three team members listed above with a specific pitch. They're a great group of positive people to work with.
If you need help with generating a topic idea, writing an article, proofreading, etc., please feel free to reach out to me. I've been writing professionally for about 15 years, and I'm happy to help out in any way I can.
Hope that helps clear things up a little!