'Stronghold' in the Bible

Then he left them with the king of Moab; and they stayed with him all the time that David was in the stronghold.

Then the prophet Gad said to David, “Do not stay in the stronghold; leave, and go into the land of Judah.” So David left and went into the forest of Hereth.

David gave Saul his oath; and Saul went home, but David and his men went up to the mountain stronghold.