The multiverse is made up of many dimensions, and the Astral Plane is the path to most.

Unearthed Spoils #009 - Dimensional Delves contains the following content:

• OATH OF THE ELEMENTAL PLANES - Elite champions of primordial beings, these paladins hold faith in planar elements.
• WAY OF PLANAR ENERGY - These monks finesse a balance between the Planes of Positive and Negative Energy.
• BACKGROUND: PLANAR BORN - Your natural talents are out of this world.
• DIMENSIONAL DWOEMERS - Add some magic from the multiverse to your repertoire.
• OTHERWORLDLY OBJECTS - These enchanted items were forged with inter-dimensional magic.
• DIMENSIONAL DENIZENS - Planar beings add inter-dimensional spice to your world.
• 7th-LEVEL ADVENTURE - A ringworld’s reason for being is threatened by a growing gap in its magic. The Tablets of Tu’faeyel must be recovered soon, or they will close many of the world’s gates.