Noun
S-box (plural S-boxes)
(cryptography) A basic component of symmetric-key algorithms, which performs substitution, transforming one set of bits into another.
In block ciphers, S-boxes are typically used to obscure the relationship between the key and the ciphertext.
A good P-box has the property that the output bits of any S-box are distributed to as many S-box inputs as possible. Source: Internet
For example, with the current S-box AES emits no fixed differential with a probability higher than (4/256) 50 or 2 −300 which is far lower than the required threshold of 2 −128 for a 128-bit block cipher. Source: Internet
This continues, replacing the entire P-array and all the S-box entries. Source: Internet