Dungeons & Dragons campaign settings

The flexibility of the Dungeons & Dragons (D&D) game rules means that Dungeon Masters (DM) are free to create their own fantasy campaign settings. For those who wanted a pre-packaged setting in which to play, TSR, Wizards of the Coast (WotC), and other publishers have created many settings in which D&D games can be based; of these, the Forgotten Realms, an epic fantasy world, has been one of the most successful and critically acclaimed settings.

Source: Wikipedia — Dungeons & Dragons campaign settings (CC BY-SA 4.0)