Wall kick

A wall kick happens when a player rotates a tetromino when no space exists in the squares where that tetromino would normally occupy after the rotation. To compensate, the game sets a certain number of alternative spaces for the tetromino to look.

Koryan as well as Jagorochi researched the SRS system thoroughly and made diagrams of how SRS finds wallkicks.

The complete system for a number of Tetris games exists in wktables.c within open-source Lockjaw.