A disk image is a file that contains a complete copy of the data from a storage device, such as a hard drive or a CD. It captures everything, including the file system, files, and metadata, allowing users to replicate or back up the original device. Disk images are often used for software distribution, system backups, and data recovery. These images can be created using various software tools and are typically saved in formats like ISO or IMG. Users can mount disk images to access their contents without needing the original physical media, making them a convenient solution for managing data.