dirified

The basename is dirified (spaces replaced by underscores, other punctuation removed) in order to create a valid URL.

--Movable Type 3.2 User Manual: Entry basename

Anil Dash says: "Dirified just means that it gets rid of any characters or symbols that couldn't appear in a directory name, and then shortens the whole thing about 15 characters." The term appears to be in very limited use.