The tetrion is the frame that surrounds the playfield. Henk Rogers has defined "tetrion" as the machine that plays Tetris.[1]

Different tetrions may implement different variations of the game rules. For example, TAP indicates the game mode with different frame colors:

Easy

Master

T.A. Death

TGM+

In Tetris Worlds, tetrions are described as gateways which, when opened, give the Minos access to a new planet in their galaxy suitable for terraforming.