What does MD5 mean? The MD5(Message-Digest algorithm 5) algorithm is used as an encryption or fingerprint function for a file. MD5Encryption.com allows you to enter a word to encrypt MD5 hashes for free. What is an MD5 hash, or MD5 Checksum? MD5 is a 128-bit message digest function. It is used commonly in user authentication and MD5 checksum for data integrity. Many big websites use MD5, sites lik