ma·re clau·sum /ˈmɑr(ˌ)eˈklaʊsəm, ˈklɔ-/
Ma·re clau·sum Internat. Law Lit., closed sea; hence, a body of water within the separate jurisdiction of the nation; -- opposed to open sea (mare liberum), the water open to all nations and over which no single nation has special control.
n : (closed sea) a navigable body of water under the
jurisdiction of a single nation