'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.

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

David swore to Saul. And Saul went to his home, but David and his men went up to the stronghold.