Apple Disk iMaGe file format

This proprietary Mac OS file disk image format (the term "image" refers to copied data, not to a picture or graphic) is most commonly used to distribute macOS-compatible software over the Internet. It allows secure password protection as well as file compression and hence serves both security and file distribution functions. It is based on the Universal Disk Image (UDIF), a flat file format which is the native image format for macOS.