The Seven Kingdoms of Westeros, simply known as the Seven Kingdoms, is a realm on the continent of Westeros. As the name suggests, it is a series of kingdoms with restricted autonomy that answer to the Lord of the Seven Kingdoms, the king who sits on the Iron Throne in the capital city, King's Landing. The name originated from the period prior and following Aegon's conquest, when Westeros was divided between seven, independent and autonomous kingdoms that Aegon Targaryen then conquered and united under one rule. The new realm created under House Targaryen contains nine distinct regions or provinces.
When Aegon finished his conquest, he had only conquered six of the seven kingdoms of the realm: Dorne had been the only faction to successfully resist Aegon's influence. It would not be until Daeron II Targaryen that Dorne would join as the seventh kingdom of the realm.