Optical see-through head-mounted display
An optical see-through head-mounted display (OST-HMD) is a wearable device that has the capability of reflecting projected images as well as allowing the user to see through it, in contrast to typical head-mounted displays, which still use optical components, but are not see-through, such as virtual reality headsets. In some cases, this may qualify as augmented reality (AR) technology.
Source: Wikipedia — Optical see-through head-mounted display (CC BY-SA 4.0)