What is "a closed sea"

Close \Close\ (kl[=o]z), v. t. [imp. & p. p. Closed (kl[=o]zd); p. pr. & vb. n. Closing.] [From OF. & F. clos, p. p. of clore to close, fr. L. claudere; akin to G. schliessen to shut, and to E. clot, cloister, clavicle, conclude, sluice. Cf. Clause, n.]

1. To stop, or fill up, as an opening; to shut; as, to close the eyes; to close a door.

2. To bring together the parts of; to consolidate; as, to close the ranks of an army; -- often used with up.

3. To bring to an end or period; to conclude; to complete; to finish; to end; to consummate; as, to close a bargain; to close a course of instruction.

   One frugal supper did our studies close.
   --Dryden.

4. To come or gather around; to inclose; to encompass; to confine.

   The depth closed me round about.
   --Jonah ii.

5. But now thou dost thyself immure and close In some one corner of a feeble heart.
   --Herbert.

   A closed sea, a sea within the jurisdiction of some particular nation, which controls its navigation.