Temporary Profile
From Halopedia, the Halo wiki
A temporary profile is used in Halo 3, for players/users that have not created a profile and wish to play the Multiplayer the Campaign. When a player without a profile signs into a game, he/she will be asked if they would like to use a temporary profile.
Temporary profiles cannot be saved. When you receive a temporary profile, you are issued a random username and tag. Examples are "Devious" and "Sparty".
