MD5 (Message Digest Algorithm) is a cryptographic hash algorithm.

The algorithm takes as input a message of arbitrary length and produces as output a 128-bit "fingerprint" or "message digest" of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given prespecified target message digest. The MD5 algorithm is intended for digital signature applications, where a large file must be "compressed" in a secure manner before being encrypted with a private (secret) key under a public-key cryptosystem such as RSA.1?

Basically MD5 is an easy way to verify the integrity of a peice of data.

Some common uses of MD5 are for

• HashTable
• PasswordEncryption
• Making long strings shorter

http://userpages.umbc.edu/mabzug1/cs/md5/md5.html

1? RFC:1321