From PathfinderWiki
The Planes
The planes of reality, also called the Great Beyond or multiverse, are unimaginably vast and varied. Much about the planes is unknown; that which is known is presented below.
The Solar System of Golarion
The SunAballon, the HorseCastrovel, the Green PlanetGolarion, the ChildAkiton, the Red PlanetVerces, the LineThe DiasporaEox, the Dead PlanetTriaxus, the WandererLiavara, the DreamerBretheda, the CradleApostae, the MessengerAucturn, the StrangerSolar system.jpg
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The Universe, also known as the Material Plane, is effectively infinite for the majority of its known inhabitants. The majority of the plane's volume is believed to the be the void known as the Dark Tapestry, while the remainder consists of stars, planets, and other celestial bodies such as comets, asteroids, and meteors.

More information about the Universe and its elements:

Planes of the multiverse are effectively infinite. Indeed, many planes have layers which are also infinite. They are grouped to simplify our understanding of how they relate to one another.

The Great Beyond attempts to discuss the relationships between the planes of the Inner Sphere, the Transitive planes, and those of the Outer Sphere.

More information about types or groups of planes can be found here:

Demiplanes are finite. Most demiplanes are created by powerful magic or natural processes and often temporary, though they are sometimes made permanent through further magical processes.

More information about some of the notable demiplanes can be found here: