Tetradroids are game pieces shaped like tetrominoes, geometric shapes composed of four square blocks each. A random sequence of Tetradroids fall down the playing field (a rectangular vertical shaft, called the "well" or "matrix"). The objective of the game is to manipulate these Tetradroids, by moving each one sideways and rotating it by 90 degree units, with the aim of creating a horizontal line of ten blocks without gaps. When such a line is created, it disappears, and any block above the deleted line will fall. When a certain number of lines are cleared, the game enters a new level. As the game progresses, each level causes the Tetradroids to fall faster, and the game ends when the stack of Tetradroids reaches the top of the playing field and no new Tetradroids are able to enter. Some games also end after a finite number of levels or lines.