Motion Capture & Motion Tracking

MoCap, short for motion capture, is a technique used to digitally record movement. In art, it's a powerful tool that allows creators to translate physical gestures into digital data that can be used across many digital art forms. Mocap can be recorded or used in realtime in contemporary art, performance, and installation work. 

Motion Tracking is used to follow the movement of a specific object, body part, or point — often in real time — but not necessarily capturing full-body motion or saving a performance.

In short:
MoCap is about capturing a performance.
Motion tracking is about responding to movement.