A Head-Mounted Display (HMD) is a device worn on the head that provides visual and auditory experiences directly in front of the user's eyes and ears. HMDs are commonly used in virtual reality (VR) and augmented reality (AR) applications, allowing users to immerse themselves in digital environments or overlay digital information onto the real world. These devices typically consist of two small screens, one for each eye, and may include built-in headphones for sound. HMDs can track head movements, enabling users to look around in a virtual space. Popular examples of HMDs include the Oculus Rift, HTC Vive, and Microsoft HoloLens.