Equipment
From Halopedia, the Halo wiki
In Halo 3, Spartans, Brutes and Elites, can carry one extra item of equipment – deployed using the “X” button on the controller. Equipment types vary dramatically in purpose, functionality and appearance, but all can be used with deadly or strategic force. To follow is a simple explanation of what each does, and where you can find at least one of them. There may be more to find and their availability is subject to matchmaking rules.
The philosophy of equipment is simple – add variety to the combat in Halo 3 without displacing balance. The simple fact is that Equipment items, once deployed can be used by both attackers and defenders. Someone on your team might accidentally activate your Trip Mine, and a Bubble Shield is a geometric spherical shield – sure they can’t shoot in, but you can’t shoot out either. Suffice to say that equipment can turn the tide of battle if used correctly. To make it more balanced, it takes longer to deploy equipment than in the Halo 3 Beta, but you can launch it farther. It is not entirely clear which faction - Human or Covenant - manufactures each piece of equipment in the first place without doing research on the specific equipment, as both are seen utilizing it in the single player campaign.
