Multithreading in games means distributing work across multiple CPU cores simultaneously. The traditional game loop is single-threaded: update physics, then AI, then gameplay, then render -- all in sequence. Modern games split this work across threads: the physics engine runs on one core while AI updates on another, audio mixes on a third, and the renderer prepares draw calls on a fourth. The challenge is synchronization -- threads that share data need to coordinate access without creating race conditions (two threads writing to the same data simultaneously) or deadlocks (two threads waiting for each other forever). Job systems, where work is broken into small tasks that any available core can pick up, have become the dominant approach. Unity's DOTS and Unreal's task graph both use this model.