For questions about the creation and use of disk images - raw data from a storage medium that has been extracted into a file.
Disk images are files the hold block-by-block copies of physical media. Sources include floppy disks, hard drives, and optical media.
Some formats are "raw", i.e. they contain nothing but the blocks from the source. Others include headers with meta-data, and may compress the data to reduce space.
In retrocomputing, disk images are frequently used in conjunction with emulators.