Rotate
In Tetris games, the player must rotate the tetraminos, changing their orientation so that they will fit into the well in advantagious positions. Most (all?) official or quasi-official Tetris games give the player the ability to rotate a tetramino either clockwise or counterclockwise as many times as the player can before it locks. All seven of the tetraminos can be rotated, including the O piece (which has only one orientation).