a technique in computer graphics where background images move past the camera more slowly than foreground images, creating an illusion of depth in a 2D scene of distance.

A vertically scrolling video game or vertical scroller is a video game in which the player views the field of play principally from a top-down perspective, while the background scrolls from the top of the screen to the bottom (or, less often, from the bottom to the top) to create the illusion that the player character is moving in the game world.