What does "redoubt" mean?

Redoubt: (a) A small, and usually a roughly constructed, fort or outwork of varying shape, commonly erected for a temporary purpose, and without flanking defenses, -- used esp. in fortifying tops of hills and passes, and positions in hostile territory. (b) In permanent works, an outwork placed within another outwork. See F and i in Illust. of Ravelin. [Written also redout.]