Board Thread:General Discussion/@comment-5254530-20140406203815/@comment-366087-20140408050644

Autoconfirmed is a "background" group almost all users have after 4 days and a few edits. One of the things it is used for which you may have seen is protections; the level between None(All Users) and Full(Admins only) is Semi(Autoconfirmed and Registered).

Normally it is invisible, but something about Hawk's script and unconfigured UserTags reveals the "invisible" groups.