A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet (see helmet-mounted display for aviation applications), that has a small display optic in front of one (monocular HMD) or each eye (binocular HMD). HMDs have many uses including gaming, aviation, engineering, and medicine.[1]
Virtual reality headsets are a type of HMD that track 3D position and rotation to provide a virtual environment to the user. 3DOF VR headsets typically use an IMU for tracking. 6DOF VR headsets typically use sensor fusion from multiple data sources including at least one IMU.
An optical head-mounted display (OHMD) is a wearable display that can reflect projected images and allows a user to see through it.[2]