In StarCraft, the Terran marine's powered combat armor is called CMC-300 armor.
The CMC-300 is the standard powered suit associated with Terran Marines in the original StarCraft setting. It provides protection, life support, strength enhancement, and the equipment mounting needed for a marine's battlefield weapons. The suit helps ordinary human infantry operate in hostile environments and survive combat against the Protoss and Zerg.
The designation is easy to confuse with names of Terran vehicles and weapons. CMC-300 refers to the armor system, not the marine's gauss rifle, a siege tank, or a different infantry class. Later StarCraft fiction and game material mention several armor variants, but the classic Marine suit is conventionally identified as the CMC-300.