The Dungeons & Dragons Settings are composed of a large number of (mostly) independent game worlds and settings, each of which uses the D&D rules (or some variant of them).
The various Dungeons & Dragons settings are connected to each other through Wildspace and the Phlogiston, enclosed in crystal spheres. Beyond the Prime Material plane, there are many other planes of existence. These are frequently collectively grouped as Planescape. The other planes of existence mostly fall into three categories: the Prime Material plane and demi-planes, the Inner planes (largely elemental planes) and the outer planes (heavens, hells, and so forth).
Note that because of the differences in both setting and the significant changes to many creatures, the 4th edition Dungeons & Dragons is not included in this meta-setting.Settings within Dungeons and Dragons Settings: