The region south of Egypt, in essence, Nubia or Northern Sudan. Originally the name of a district somewhere between the second and third cataracts of the Nile (about 2000 B.C.), "Kush" became also a general term for Nubia among the Egyptians, which wider use Hebrews, Assyrians and others took over.
Throughout Isaiah (11:11; 18:1); 20:3-5; and 43:3; 45:14), Egypt and Ethiopia are closely linked--for in the prophet Isaiah's time the "Ethiopian" 25th Dynasty ruled over both. [Tyndale House, The Illustrated Bible Dictionary, Vol. 1, pp. 349-350]
2 Nephi 21:11 Cush ([Illustration]): Old Testament Africa. [Tyndale House, The Illustrated Bible Dictionary, Vol. 1, p. 18]