Tetris is a block-stacking game published by Bullet-Proof Software, Inc. The goal is to place pieces made up of four tiles in a ten-by-twenty well, organizing them into complete rows, which then disappear. The goal of each round is to clear 25 lines, after which the player moves on to the next round. If the stack reaches the top of the field, the player loses a life, and if all three lives are lost, the game is over.