Easton’s Bible Dictionary
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 (which see) separating it from Moriah (which see), which it surpasses in height by 1 Chronicles 105 feet. It was the south-eastern hill of Jerusalem.
When David took it from the Jebusites (Joshua 15:63; 2 Samuel 5:7) he built on it a citadel and a palace, and it became "the city of David" (1 Kings 8:1; 2 Kings 19:21,31; 1 Chronicles 11:5). In the later books of the Old Testament this name was sometimes used (Psalm 87:2; 149:2; Isaiah 33:14; Joel 2:1) to denote Jerusalem in general, and sometimes God's chosen Israel (Psalm 51:18; 87:5).