ACL UOP
The UOP level is for general regular users of a channel, users on this list will be set CMODE +u when joining the channel. While this mode doesn't give any power, it allows the user to look at the access lists, invite himself into the channel if a channel mode prevents joining, and to receive channel memos.
UOP is the lowest level of access and usually just serves as a first recognition of a regular user, who might then become VOP after a certain time.