A guest is a character to which anyone can connect to investigate a multiplayer world. On an MU*, this is usually done by typing connect guest guest. An MU usually has a few guest characters, so that more than one guest can be connected simultaneously.
Guest characters are often restricted to a particular area, such as an OOC nexus. They can read help and news files, and interact with other players. They are anonymous to the general public on the MU*, but wizards can see their IP address if desired.