Territorial water

Territorial waters, in international law, that area of the sea immediately adjacent to the shores of a state and subject to the territorial jurisdiction of that state. Territorial waters are thus to be distinguished on the one hand from the high seas, which are common to all countries, and on the other from internal or inland waters, such as lakes wholly surrounded by the national territory or certain bays or estuaries. The concept originated in the 17th-century controversy over the status of the sea. Though the doctrine that the sea must be accessible to all was upheld, a nation’s jurisdiction over its coastal waters was also recognized. Nations subscribing to the Law of the Sea observe a territorial limit of 12 nautical mi (22 km) from shore. Territorial rights include the airspace above those waters and the seabed below them [Encyclopaedia Online Britannica].
The area of sea around the coast of a country is thought to belong to it, often going out to twelve nautical miles [Cambridge Online Dictionary].

Sources:

Territorial waters. Cambridge Online Dictionary. Retrieved from: https://dictionary.cambridge.org/dictionary/english/territorial-waters

Territorial waters. Encyclopaedia Online Britannica. Retrieved from: https://www.britannica.com/topic/territorial-waters