The Multiverse

The Multiverse is made up of trillions of different parallel universes. These universes are either created artificially through Time Travel, or naturally through the timeline splitting when certain huge decisions are made. There is no way to know the exact number of universes, but it's definitely not infinite as White Chara was once able to kill every parallel Chara in existence by traveling from universe to universe.

Every universe is connected through the Void, a dark, mostly empty plane between the dimensions. Most universes are also known to hold a few sub-dimensions.

In the main universe there's the Mortal Plane, three Death Realms, The Angel and Demon Realms, Wish Dimension, God Realm and QRA.

It should be noted however, that these were all created at some point in time so there should statistically be universes out there without them.

Travel between the universes is difficult, but not impossible as seen by: Gascoin, White Chara, Titanus, Twelve, Mickolash and a few other powerful individuals.

The multiverse is housed inside the Bubbleverse, which in turn is part of the Lightverse.