Dimensions is an area with specific generation rules. In Hexxit, there are the four major dimensions and one minor dimension that contains a lot of possibilities from Dimensional Doors.
The overworld is the main dimension the player enters a new world into and contains the most biome types, mobs, and is most commonly the dimension used for player bases.
The End Edit
Twilight Forest Edit
Twilight Forest is a dimension added by a mod of the same name, and consists of a lot of forest based biomes, unique dungeons and bosses.
Pocket Dimensions Edit
Pocket Dimensions are added by Dimensional Doors. They are small rooms with nothing but blackness. These dimensions can often be found with pre-made dungeons when going through a pocket dungeon.