'Strongholds' in the Bible

The men of Israel realized they had a problem because their army was hard pressed. So the army hid in caves, thickets, cliffs, strongholds, and cisterns.

David stayed in the strongholds that were in the desert and in the hill country of the desert of Ziph. Saul looked for him all the time, but God did not deliver David into his hand.

Then the Ziphites went up to Saul at Gibeah and said, "Isn't David hiding among us in the strongholds at Horesh on the hill of Hakilah, south of Jeshimon?

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