Head tracking refers to software detection and response to the movement of the user’s head. Typically, it’s used to move the images being displayed so that they match the position of the head. Most XR headsets have some form of head tracking in order to adjust their visual output to the user’s point of view.
Orientation tracking uses accelerometers, gyroscopes, and magnetometers to determine how the user’s head is turned. Position tracking systems, like those in the HTC Vive or the HoloLens, require extra sensors set up around the room.