+**Concave** describes a surface or [curve](/wiki/curve) that bulges inward, like the inside of a sphere. When viewed from outside, it appears to curve away from the observer, creating a hollow or bowl-like [shape](/wiki/shape).
+## See also
+- [Convex](/wiki/convex)
+- [Geometry](/wiki/geometry)
+- [Optics](/wiki/optics)
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