A water tunnel or channel that carries water from one place to another. In the Old Testament, the Hebrew word can mean two things:
Small streams in the ground made by rain. In Job 38:25, called a “channel.” In Ezekiel 31:4, called a “stream.”
A simple trench like the one Elijah dug around the altar during his challenge against the prophets of Baal. Baal was a Canaanite god of fertility (1 Kings 18:31–38).
King Hezekiah constructed a water tunnel. He did this to bring water from the Gihon Spring to inside the city. The Bible also refers to this spring as a “pool” (2 Kings 18:17; 20:20; Nehemiah 2:14; Isaiah 7:3; 22:9–11; 36:2). The spring was originally outside the city walls, which was dangerous during enemy attacks. Hezekiah's workers sealed the spring's opening and created a tunnel to bring the water safely inside the city.
The tunnel built by Hezekiah expanded an earlier tunnel that was started by the Jebusites. The Jebusites lived in Jerusalem before the Israelites. King David and his men may have entered Jerusalem through the first tunnel to defeat the Jebusites (2 Samuel 5:8).