The following image shows a simple example of six images that make up a game's background panorama: you see the top (blue sky), the bottom (the ground), and four sides (a snow-covered mountain at the horizon).
The trick with skies is that you project these six textures onto the insides of a gigantic cube that encompasses your whole scene. This popular approach of faking a background is called
environment mapping. When we use a six-image
CubeMap to simulate a sky, we refer to the box as
You can create your own SkyBox from a vacation photo or poster in a graphic editor: