凹
āo
concave; sunken
Every meaning
āo
- concave; sunken
- (slang) to pose for a photo (as in 凹造型)
wā
- (used in place names) hollow; low-lying land
Meanings are from Mandarin The Wild’s own dictionary. Levels follow the official HSK word list (the exam’s 2025 syllabus, levels 7–9 shown together).