Tetris is composed of a field of play in which pieces of different geometric forms, called "tetriminos", descend from the top of the field. During this descent, the player can move the pieces laterally and rotate them until they touch the bottom of the field or land on a piece that had been placed before it. The player can neither slow down the falling pieces nor stop them, but can accelerate them. The objective of the game is to use the pieces to create as many horizontal lines of blocks as possible. When a line is completed, it disappears, and the blocks placed above fall one rank. Completing lines grants points, and accumulating a certain number of points moves the player up a level, which increases the number of points granted per completed line. The player can clear multiple lines at once, which can earn bonus points. It is possible to complete up to four lines simultaneously with the use of the I-shaped tetrimino; this move is called a "Tetris", and is the basis of the game's title. If the player cannot make the blocks disappear quickly enough, the field will start to fill, and when the pieces reach the top of the field and prevent the arrival of additional pieces, the game ends.