An MD5 file is a checksum file used to verify the integrity of a disc, disk image, or a downloaded file. It stores a checksum, which is a value created from an algorithm based on the number of bits in the file. MD5 files are sometimes generated when a disk image is created.

MD5 files function similarly to human fingerprints. They are unique and are used to verify identity. This is especially important for security reasons in case a file is changed for malicious purposes or corrupted from a disk error or incomplete file transfer. NOTE: Standard MD5 checksums are 32 characters long, which requires 16 bytes or 128 bits.