.M3 File Extension

3D model used by StarCraft II: Wings of Liberty, a sci-fi real-time strategy game; created in Blizzard's MDX3 format, which is the successor to the .MDX file format used in Warcraft 3 and the .M2 format used in World of Warcraft; used for storing models for game units and structures for the Protoss, Terran, and Zerg races; also used for other game objects.

M3 files are commonly found within in .SC2ASSETS files, which are stored in Blizzard's .MPQ format.