Zion

sunny; height, one of the eminences on which Jerusalem was built. It was surrounded on all sides, except the north, by deep valleys, that of the Tyropoeon (q.v.) separating it from Moriah (q.v.), which it surpasses in height by 105 feet. It was the south-eastern hill of Jerusalem.

When David took it from the Jebusites (Josh 15:63; 2Sam 5:7) he built on it a citadel and a palace, and it became "the city of David" (1Kings 8:1; 2Kings 19:21; 19:31; 1Chr 11:5). In the later books of the Old Testament this name was sometimes used (Ps 87:2; 149:2; Isa 33:14; Joel 2:1) to denote Jerusalem in general, and sometimes God's chosen Israel (Ps 51:18; 87:5).

In the New Testament (See SION) it is used sometimes to denote the Church of God (Heb 12:22), and sometimes the heavenly city (Rev 14:1).

EBD - Easton's Bible Dictionary