The kanji character 凹 primarily represents a concavity, indentation, or a hollowed-out area. It signifies a recessed or sunken shape, the opposite of convexity or protrusion. It's often used to describe a dip or depression in a surface.

・On-yomi (音読み): オウ (ō) ・Kun-yomi (訓読み): くぼ（む） (kubo(mu)) - to be dented, to be concave; くぼ（み） (kubo(mi)) - a dent, a hollow

⚫︎ 凹凸 (ōtotsu) Translation: unevenness; irregularities; concavity and convexity ⚫︎ 凹面鏡 (ōmenkyō) Translation: concave mirror ⚫︎ 凹む (kubomu) Translation: to be dented; to be sunken; to cave in

The kanji 凹 is a pictograph. It depicts the shape of something that is indented or hollowed out. The two lines at the top likely represent the surface level, and the depression below symbolizes the indentation itself. The character directly reflects the physical concept it represents. The shape is intuitive and has remained relatively unchanged over time.