An integrated setting is a setting that is presented in a role-playing game's rulebook and is so thoroughly connected with that game's rules and game mechanics that the game can't be played in any other setting without extensive hacking.
Integrated settings are extreme versions of default settings (in that they are also presented in a game's rules and assumed to be the setting that any group will use) and implicit settings (in that the rules dictate certain details about the settings, but for an integrated setting that is more extreme).