Winter Bash (holiday hats) celebration at the end of each year. Use this tag for Apps, Scripts, or API questions that enhance the Winter Bash experience.

Winter Bash is a special celebration that typically runs from December 15th until January 4th each winter (2012, 2013, 2014, and almost certainly beyond).

Users who participate earn hats for their avatar, via various acts on Stack Exchange sites.

Here's a sample of user avatars wearing hats:

Haberdashery

Reference: