There is only one file type that uses the .MD5 extension:
MD5 Checksum File
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.
Updated: May 23, 2018