A Head-Mounted Display (HMD) is a device worn on the head that features a small screen in front of the eyes. It allows users to experience virtual reality or augmented reality by immersing them in a digital environment. HMDs often include sensors to track head movements, enhancing the sense of presence in the virtual world. These displays are commonly used in gaming, training simulations, and medical applications. Popular examples of HMDs include the Oculus Rift, HTC Vive, and Microsoft HoloLens. They can provide interactive experiences by combining visual and auditory elements, making them valuable tools for entertainment and education.