The Material Plane, also called the Prime Material Plane, is the primary world where most Dungeons & Dragons adventures take place.
According to one interpretation of cosmology, there are infinite parallel material planes, each its own separate world. A more recent interpretation is that there is one Material Plane, and all of these worlds exist within it.
The Material Plane is most adventurers' benchmark for planar norms. Therefore, for example, it has normal gravity by definition, and the gravity all other worlds is measured relative to the Material.