au凹

concave

concave; hollow; sunken; dented; to cave in; to be sunken; to dent; to be concave; indentation; depression; swollen bumps on the skin

English Wiktionary, “凹” (CC BY-SA 4.0) — https://en.wiktionary.org/wiki/%E5%87%B9 · confidence: Medium (Wiktionary)