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A tetromino's orientation, with regards to Tetris refers to the different ways that tetromino can exist after rotations.
Normally all the tetrominoes have a total of nineteen orientations, but probably to make things more symmetric, newer games add six orientations: two for S, Z, and I.
Orientations can be described either by the way they point (especially for T, which at least one reviewer has compared to a finger gesture (link - NSFW, 18+)) or by the way the longest flat side faces.