I'm thinking we should rename this tag to "April Fools' Day" or "April Fools' Day Posts" and add a description. (Seriously.)
After some discussion with Pablo, I've renamed this tag to "Humor". People sometimes write humorous posts on other days, and it seems excessive to have an "April Fools' Day" tag in addition to a "Humor" tag. It's easy enough to see which "Humor" posts were written on April Fools' Day if someone wants to.
This change isn't set in stone -- I'm open to arguments that we should have an AFD-specific tag.