|Out of date.|
|It has been superseded by something that has been published elsewhere.|
Unlike its name would imply, a world is not necessarily related to a large planetary object. In the case of games, we use world to refer to a subset of the Gameworld in which there is a thematic unity as well an that a specific subset of the game mechanics used throughout an entire game come into play. Usually, a world is a series of levels that are tied together in some way. This binding can be expressed notationally, spatially, artistically, thematically and by gameplay.
While older games tend to favor the notion of world as a grouping of levels, newer games generally eschew this while still maintaining the concept of world. In this case, we refer to world as a large gameworld space where the player must complete a diverse number of objectives. Each world is different from another world in much the same way as was described previously (as in, thematically, gameplay, artistically, etc.) however the distinction is that there are no distinct levels within. This is an approach that has also been taken by more recent platformer-style games (such as Jak and Daxter) where the player is presented with a large seamless world even if there are notable areas where gameplay and theme are different.
In fact, what helps determine if a game is using this concept or not is whether levels are grouped together and how distinctive or strong that grouping is. For example, many traditional console platformer games are structured as a series of worlds, each with a series of levels. Different worlds are distinguishable from each other thanks to distinct visual stylings as well as different gameplay considerations. In a typical Ice World, all the levels have ice and snow and surfaces are slippery making the player controlled character harder to control due to inertia in the movement. Enemies in this level are also suited to the frigid environment. It is also common for the last level in a world to be some sort of boss level. (see Boss Level)
In Kingdom Hearts (PS2) there is not only a depiction of interplanetary travel, but also a strong thematic element tied to each of the worlds. Each world is inspired by different Disney movies such as Tarzan, The Little Mermaid and Alice in Wonderland.
Different worlds introduce new game mechanics that are sometimes used only in the particular world in which they are introduced. For example, in Atlantica (the Little Mermaid inspired world), the player must learn how to swim in order to move
Kingdom Hearts is a strong example of the use of worlds even though there is no grouping of levels because the spatial locations are so markedly different and have different gameplay implications.
Weak Example In Half-Life, the player spends most of his time in one of two places: Black Mesa Research complex and Xen (another dimension). There are clear gameplay differences between Xen and Black Mesa Research in particular due to variations in the gravity. This greatly affects the way the player moves. Given that Xen is an alien dimension, everything looks different and unfamiliar.
This is a weak example because despite the significant differences between worlds, the majority of the game takes place in Black Mesa research with Xen only being introduced at the end of the game.