Advanced Encryption Standard (AES)
The cryptographically stronger successor to the Data Encryption Standard (DES); the selection of the AES algorithm involved submissions from around the world and was overseen by the US government's National Institute of Standards (NIST). It was adopted by NIST in May of 2002.
Sub Bytes
A non-linear substitution step where each byte is replaced with another according to a lookup table.
Shift Rows
A transposition step where each row of the state is shifted cyclically a certain number of steps.
Mix Columns
A mixing operation which operates on the columns of the state, combining the four bytes in each column.
Add Round Key
Each byte of the state is combined with the round key; each round key is derived from the cipher key using a key schedule.
Key Scehdule
For keys 128 and 192 bits in length, the subkey material, which consists of all the round keys in order, consists of the original key, followed by stretches, each the length of the original key, consisting of four-byte words such that each word is the XOR of the preceding four-byte word and either the corresponding word in the previous stretch or a function of it. For the first word in a stretch, the word is first rotated one byte to the left, and then its bytes are transformed using the S-box from the Byte Sub step, and then a round-dependent constant is XORed to its first byte.
Additional Links
Wikipedia
Presentation of AES
Another AES applet
Images taken from wikipedia see link above