mare clausum

from The Century Dictionary.

• noun A closed sea; a sea closed to navigation; a sea or a part of the high seas within the jurisdiction of a particular nation, as distinguished from the open sea, where all nations have equal right.

from the GNU version of the Collaborative International Dictionary of English.

• (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.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (closed sea) a navigable body of water under the jurisdiction of a single nation