Message Digest 5 (MD5) creates a fixed size cryptographic string which represents the message. This output is known as digest. The resulting hash/digest is one-way and cannot be reversed. It takes the message, applies the MD5 algorithm, and outputs a 128-bit value. This digest is sent together with the message to its intended destination.
MD5 contains collision vulnerabilities. A collision vulnerability/attack is where two or more entirely different files produce the same hash/digest. An MD5 collision occurred in 2008.