Sea

the, (Heb. yam), signifies

(1) "the gathering together of the waters," the ocean (Gen 1:10);

(2) a river, as the Nile (Isa 19:5), the Euphrates (Isa 21:1; Jer 51:36);

(3) the Red Sea (Ex 14:16; 14:27; 15:4), etc.;

(4) the Mediterranean (Ex 23:31; Num 34:6; 34:7; Josh 15:47; Ps 80:11), etc.;

(5) the "sea of Galilee," an inland fresh-water lake, and

(6) the Dead Sea or "salt sea" (Gen 14:3; Num 34:3; 34:12), etc.

The word "sea" is used symbolically in (Isa 60:5), where it probably means the nations around the Mediterranean. In (Dan 7:3; Rev 13:1) it may mean the tumultuous changes among the nations of the earth.

EBD - Easton's Bible Dictionary