I tried to write a meta post about winter bash and hats, but I couldn't find any simple explanation page to link to. I ended up garbling a home-spun description of my own with a not-terribly-helpful image from 2012.
This comment on a separate Meta.math.se thread puts it better than I can:
As a new user in 2015 can there please be more information about what is WinterBash. The link took me to a bunch of stick figures running around making (I think) numbers (I think its a countdown clock). It doesn't explain the event or even what a hat is. – Ian Miller Dec 4 at 2:58
All I found on Meta was dead links. For example, What is Winter Bash all about? was downvoted to -2 and answered with a link to an FAQ page that no longer exists.