Curvature

Curvature describes how a curve or surface bends or deviates from being flat or straight. For a line, if it’s perfectly straight, its curvature is zero. If it bends, like a circle, the curvature indicates how tight the bend is—the tighter the bend, the higher the curvature. On surfaces, curvature helps describe how the surface curves in different directions, such as a sphere (which is curved in all directions) versus a saddle shape (curving up in one direction and down in another). In essence, curvature quantifies the degree and nature of bending in geometric objects.