Curvature refers to the amount by which a curve deviates from being a straight line or a surface deviates from being flat. In mathematics, it is a measure of how much a geometric object bends. For example, a circle has constant curvature, while a straight line has zero curvature. In physics, curvature can describe the shape of space and time, especially in the context of Einstein's theory of general relativity. Here, massive objects like planets and stars cause the fabric of space-time to curve, affecting the motion of other objects nearby.