'Stronghold' in the Bible

So he had them stay with the king of Moab; they stayed with him the whole time that David was in the stronghold.

Then Gad the prophet said to David, "Don't stay in the stronghold. Go to the land of Judah." So David left and went to the forest of Hereth.

David promised Saul this on oath. Then Saul went to his house, and David and his men went up to the stronghold.