For general questions about the Winter Bash (or holiday hats) celebration at the end of the year. Please consider using the year-specific variation, e.g. [winter-bash-2018] if it's solely about this year's edition of Winter Bash.

Winter Bash is a special celebration that typically runs from mid-December until early January each year. Users who participate earn hats for their avatars via various acts on Stack Exchange sites.

Here's a sample of user avatars wearing hats:

Haberdashery

Reference:

history | excerpt history