From Minecraft Wiki
Dimensions may refer to:
The Overworld - The starting dimension in Minecraft.
The Nether - The hellish dimension accessible by entering a nether portal from the Overworld.
The End - The dimension with floating end stone islands, accessible with an end portal in a stronghold.
Sky Dimension - The unimplemented dimension that would have contained floating land masses and was planned to be added in the Adventure Update.
- Dream Dimension - A briefly mentioned unimplemented then-Pocket Edition-exclusive dimension.