This is probably the most commonly used hash function. It produces a 128-bit hash. It has largely superseded earlier MD functions (for example, MD2, MD4). It is defined in RFC1321.
MD5 has been shown to be vulnerable to collisions in some applications. In SSL, it can still be used for most purposes as part of security level zero. Micro Focus recommends that you use SHA2 or SHA3 in preference to MD5.