凹面

1. Origins, structure, and basic meaning

• Structure: 凹面, read おうめん, denotes a curved surface whose center bends inward.
• Basic usage: It names the inward-curving face of a concave mirror and the bowl surface where water collects.

2. Common pitfalls and similar expressions

• An inward-curving surface
  • It is a surface curving inward at the center, the opposite of an outward convex face.