The Ekkaia or encircling Sea
Encircling Sea: ("Ekkaia"") The great ocean that encircled Arda lay south, east, and north of Middle-earth. Also called the Outer Sea, In the First Age and late Second Age it was surrounded by the Walls of Night; but, in the late Second Age. when Arda was remade as a sphere, it circumscribed and covered most of the world.
The northern Part of the Ekkaia was also known as the Frozen Sea.