HD wallpaper refers to a type of digital image that is designed to be used as a background on digital devices. The term "high-definition" refers to the image's high resolution, which is typically 1080p (1920x1080 pixels) or higher. This allows for a highly detailed and clear image that can be scaled up or down without losing quality. HD wallpapers are widely used on digital devices, including smartphones, tablets, laptops, and desktop computers.