The Rijndael S-box is a matrix (square array of numbers) used in the Rijndael cypher, also known as the Advanced Encryption Standard (AES) cryptographic algorithm. The S-box (substitution box) serves as a lookup table.
Read more about Rijndael S-box: Forward S-box, Inverse S-box, Design Criteria, An Alternate Equation For The Affine Transformation, Implementations