Head-mounted displays (HMDs) are wearable devices that are placed on the user's head and provide virtual reality (VR) or augmented reality (AR) experiences. These devices typically consist of a small screen or screens that are placed in front of the user's eyes, along with sensors and other components to track head movements and provide a realistic and immersive experience. HMDs are commonly used in a variety of fields including gaming, training, medical simulations, and more. They have the potential to revolutionize the way we interact with digital content and the world around us.