ADF stands for Amiga Disk File, a standardized file format that stores exact sector-by-sector images of Amiga floppy disks, typically 880 KB for double-density disks. It preserves the complete disk structure including boot blocks, file system metadata, and data, making it essential for software preservation and emulation. ADF files can be mounted in emulators like WinUAE or written back to physical floppy disks using tools like ADF Opus or the Amiga's own DOS commands.