Archipelagic states are states that are composed of groups of islands forming a state as a single unit, with the islands and the waters within the baselines as internal waters. Under this concept (“archipelagic doctrine”), an archipelago shall be regarded as a single unit, so that the waters around, between, and connecting the islands of the archipelago, irrespective of their breadth and dimensions, form part of the internal waters of the state, and are subject to its exclusive sovereignty.

Source: Archipelagic state – Wikipedia