Space settlements include permanent bases on other planets and moons, asteroid bases and artificial bases in space (orbital habitats, etc.). There is a considerable amount of projects already developed by space agencies that show their feasibility (example: Kaplana One project from NASA), but most of these do not take into account human trasnformation and supertechnologies (such as nano). Therefore they are too conservative and are unlikely to be realised in that form.
In the long term space settlements would be superceeded by other megascale engineering projects, such as Dyson spheres, Matryoshka brains, etc. that are built primarily for energy collection, not habitation. Terraforming will also make settlements in space possible.