'Strongholds' in the Bible

David remained in the wilderness, in the strongholds, and in the hill country in the wilderness of Ziph. And Saul sought him {continually}, but God did not give him into his hand

Then [the] Ziphites went up to Saul at Gibeah, saying, "[Is] not David hiding among us in the strongholds at Horesh on the hill of Hakilah, which [is] south of Jeshimon

David went up from there and stayed in the strongholds of En Gedi.