"Concave mirrors" refers to mirrors that have a curved surface that bulges inward, like a cave. They are curved in a way that makes objects appear larger and closer than they actually are. Full definition
The compositions flow and complement each other, combined with concave mirrors and industrial metals that manipulate the light and modify their forms. (aestheticamagazine.com)
«There are a couple of key features of the scallop's concave mirror system that make them interesting from a bio-inspired materials [development] point of view,» said Palmer. (aaas.org)