re-entrant

adjective

• (of an angle) pointing inwards. The opposite of salient.
• having an inward-pointing angle or angles.

noun

• 1a re-entrant angle: a sharp re-entrant in a material causes a local increase in stress
• an indentation or depression in terrain: they edged up a deep re-entrant to the top of the ridge

• 2a person who has re-entered something, especially the labour force: re-entrants who left to raise a family and are now seeking to get back in