凹凸不平 literally combines four characters: 凹 (āo, 'concave' or 'sunken'), 凸 (tū, 'convex' or 'protruding'), 不 (bù, 'not'), and 平 (píng, 'flat' or 'level'). Together, they describe a surface that is irregular — with both dips and bumps — making it physically uneven. It’s commonly used to describe terrain, roads, walls, floors, or any solid surface lacking smoothness.

This term carries a neutral-to-slightly-negative connotation, often implying discomfort, difficulty walking, or poor maintenance. While it can appear in technical or descriptive writing, it’s also frequent in everyday speech when complaining about rough sidewalks, unpaved paths, or worn-out furniture. Unlike simpler terms like 不平 (bù píng), 凹凸不平 emphasizes the *combination* of concavities and convexities — not just general unevenness but a visibly textured, bumpy quality.