Wraparound, in video games, is a gameplay variation on the single-screen in which space is finite but unbounded; objects leaving one side of the screen immediately reappear on the opposite side, maintaining speed and trajectory. This is referred to as "wraparound", since the top and bottom of the screen wrap around to meet, as do the left and right sides (in mathematics, this is known as a Euclidean 2-torus). Some games wrap around in some directions but not others, such as games of the Civilization series that wrap around left to right, or east and west but the top and bottom remain edges representing the North and South Pole (in mathematics, this is known as a cylinder).