What is a Secret Santa?
Traditionally, a Secret Santa is arranged among friends, coworkers, or family members during the holidays as a way to exchange gifts. Everyone puts their name and ideas of what to get them into a draw and once all the names are in, everyone randomly picks a slip of paper with someone else's name on it. On Christmas (or another time set by the organizers), everyone meets up and swaps gifts. That way, no one is excluded and you don't have to buy 20 gifts for 20 people--everyone partaking in it receives one gift per person and buys/makes one gift per person.
EmoteSecretSanta takes the same concept and puts it into place in the emote community. Everyone who wants to participate provides a list of a few things they might want to see pixelized and the organizers will randomly assign each emoticonist to make an emote from the list. In the end, everyone will have made a present for someone and received a present from someone else.