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 operating system, applications, and files, allowing for easy backup and restoration. Disk images are often used for system recovery or to create exact replicas of a device. These images can be created using various software tools and are typically saved in formats like ISO or IMG. Users can mount a disk image to access its contents without needing the original physical media, making it a convenient solution for data management and software distribution.