The Secret Santa is sort of like an art trade. But you don't know who is drawing for you. And you must keep secret who your drawing for. But everyone does a picture for someone else, and in return they get a picture from another member who is also signed up. Pictures from the 2011 secret santa can be seen in a slide show format here: http://www.youtube.com/watch?v=OpV3PUDP-8Q
More about it can be found here: http://lilymud.net/showthread.php?t=51591
This year will be the 10 year anniversary of the Lilymud Secret Santa.
EDIT: Aikachi beat me to it.
When signing up each person posts between 1 and 5 characters that they would like to see drawn. The person drawing for them has to include at least ONE of those characters in the picture. They can choose to do all 5 if they wish but at least one must be in the picture.
The mini ones are a great way to see what it is like. And meet a few other artists. This next secret santa will be a very simple one. I wont give away the theme just yet... but it is specially made so everyone should have no problem getting their picture in on time even though it is close to high school exam times.