re-entrant

adjective

1. reentering or pointing inward: a reentrant angle.

noun

2. a reentering angle or part.
3. a person or thing that reenters or returns: Reentrants to the engineering program must take the introductory course again.
4. Physical Geography. a prominent indentation in a coastline.Compare salient(def 6).

adjective

1. (of an angle, esp in fortifications) pointing inwardsCompare salient (def. 2)
2. maths (of an angle in a polygon) greater than 180° and thus pointing inwards

noun

3. an angle or part that points inwards