A Skybox is, in a nutshell, a graphical representation of the sky that 'wraps around' a computer game-world, and is used to simulate the 'sky' of a game-world. In most cases, a skybox will contain the typical aspects of what constitutes a 'sky' -- clouds, the sun, and (occasionally) birds and other avian life. Such life is usually non-interactive, and appears either as frames of static animation or as randomly generated graphical elements.

The use of a Skybox should be apparent: It allows the programmers to use relatively little memory to simulate a functioning day/night cycle and atmospheric system, even within the incredibly confined and compressed geography of a computer game (where the actual, physical distance between ground and sky may equal as little as a mile).

Skyboxes are independent graphical elements. Usually, a given skybox can be 'swapped out' for one that suits a particular setting. Some computer games come with several Skyboxes, showing different types of meteorological phenomena (such as ''aurora borealis'' or other things that can't physically be rendered) or a even an entirely different setting (apocalyptic vs. modern, for example).

Note that Skyboxes are specific to computer games; animated cartoons don't use Skyboxes, for the simple reason that there's no ''need'' to use them - the sky will naturally be drawn as part of the cartoon itself.

The Skybox may also contain 3D models that will be projected larger than life, such as distant land features or buildings-- in fact it usually does, in newer games, since it's a great way to make the world appear richer. It may even contain objects that move and change, such as the Citadel in ''VideoGame/{{Half-Life 2}}'', or even animated characters (who will appear to be distant [[{{Kaiju}} Godzillian monstrosities]], something occasionally used to good effect in {{Machinima}}.)

!! Examples
* Used in ''VideoGame/SonicAdventure2''. The levels look like they occur in the real world, but there are glitches that allow the user to jump out of a level. Doing so reveals that the levels are hallways built in a large skybox.
* In ''SpyroTheDragon'', flying outside the bounds of the flight levels reveal that you are inside a skybox.
* One of the maps in ''VideoGame/TeamFortress2'', a train-yard called "Well", uses the skybox to conceal the interiors of the teams' bases, which are BiggerOnTheInside. The top half of the buildings' façades are 3D miniatures projected onto the skybox. Generally this is not feasible in the game's engine, since the technique requires that there not be a direct line of sight to any part of the area being hidden.
* In ''VideoGame/{{Mabinogi}}: Fantasy Life'', the skybox moves as time flows; since time is sped up in the game compared to real life, you can actually watch the clouds/moon/sun move across the sky.
* A toggelable option in ''VideoGame/{{Runescape}}''. Used most notably in the Clan Citadels.
* ''VideoGame/{{Roblox}}'' has tons and tons.
* Modern [[GameEngine Game Engines]] come with built-in skyboxes; an example is Unreal Engine from EpicGames. It's most likely the first thing you see when you load up the development environment.
* Some especially enterprising ''VideoGame/KerbalSpaceProgram'' modder came up with [[http://forum.kerbalspaceprogram.com/showthread.php/44135-0-21-x-Universe-Replacer-v4-0 a utility for replacing the default skybox]], among other features.
* The Source GameEngine used by Creator/ValveSoftware supports both standard 2d skyboxes, and specialized 3d skyboxes; level designers can designate an enclosed area as the 3d skybox, which cause anything placed there to appear sixteen times larger for the rest of the map. The 3d skybox is used heavily to make the otherwise very small levels in ''Videogame/HalfLife2'' appear much larger. Some ''VideoGame/TeamFortress2'' mods can abuse the 3d skybox (which does the same thing for ''Half-Life 2'') for shits and giggles with ricocheting rockets from the Soldier, all of which can bounce off the corners of the skybox, which have a slim chance of actually hitting something.
* Wiki/SCPFoundation has [[http://www.scp-wiki.net/scp-1165 SCP-1165]], titled "Minus Level", a [[DeconstructedTrope deconstruction]] of {{Minus World}}s. There's a recreation of the Eiffel Tower in the distance, but it turns out to be part of the world's equivalent of a skybox; if one tries to reach it, they'll just notice the tower remaining at the same distance from them no matter how far they go. One survey team sent to investigate it had to call off their journey because lethal things would happen to them if they went beyond 100 km of their starting point within the strange world.