An Acronym for Advanced Encryption Standard.
A young block cipher encryption Algorithm that has replaced DES as the NSA standard recommendation after winning a competition the NSA set up. It was originally called Rijndael, after its creators Joan Daemen and Vincent Rijmen.
The name of AES was adopted after winning said competition. The finalist Algorithms were Mars, RC6, Rijndael, Serpent and Twofish. Source code and more information can be found at http://csrc.nist.gov/CryptoToolkit/aes/round2/r2algs-code.html