Noun
the angle inside two adjacent sides of a polygon
Source: WordNetA simple concave polygon has at least one interior angle that is a reflex angle. Source: Internet
Concave quadrilaterals In a concave quadrilateral, one interior angle is bigger than 180° and one of the two diagonals lies outside the quadrilateral. Source: Internet
The dihedral angle is the interior angle between any two face planes. Source: Internet