Head-mounted display on Wikipedia

A head-mounted display or helmet mounted display, both abbreviated HMD, is a display device, worn on the head or as part of a helmet, that has a small display optic in front of one (monocular HMD) or each eye (binocular HMD).

There is also an optical head-mounted display (OHMD), which is a wearable display that has the capability of reflecting projected images as well as allowing the user to see through it.