Fireteam is a gameplay mechanic found in Halo: Reach. With it, the player can recruit up to five UNSC Army, Militia, Marine and ODST troopers found through the campaign. These troopers will then follow the player throughout the level, and their status, name and rank is shown in the player's HUD next to the motion sensor. Each friendly combatant has a randomly assigned name and rank, which are not tied to their in-game character models.
Sometimes, the call sign of a member of your fireteam will change to '360', possibly a mistake or more likely a reference to the Xbox.
Fireteams usually are not very good at following the player, and often are killed quickly on higher difficulties as they are not 'trained' to deal with the situations that the player will put them in.
Be careful of what weapons you swap with your fireteam, especially heavy weapons like rocket launchers. While the versatility of a squad wielding multiple types of weapons can make or break a situation, they can still kill allies or even the player on accident.
Some of the names are from notable individuals from the Bungie Community, such as Claude Errera and Rooster Teeth.