concave surface; concavity
Refers to a surface that curves inward, like the inside of a bowl. Often used in technical contexts such as optics or geometry.
Concave mirrors are used to collect light.
noun which may take the genitive case particle 'no'
Used as a modifier (with の) to describe something having a concave shape. Common in compound terms like 凹面鏡 (concave mirror).
This lens has a concave shape.
concave mirror
Compound of 凹 (concave) and 面 (surface). The reading おうめん is the on'yomi for both characters.