Curvature is the amount that something bends or curves away from being straight or flat. A bowling ball has extreme curvature because its surface curves sharply in all directions, while a dinner plate has gentle curvature (it's mostly flat with slightly curved edges). A railroad track running straight across Kansas has almost zero curvature, but a track winding through mountain passes has lots of it.

In mathematics and science, curvature can be measured precisely. Scientists describe Earth's curvature as the way its surface gradually curves away from flat: if you could see far enough across the ocean, you'd notice ships disappearing over the horizon hull-first because of the planet's curvature. Einstein showed that massive objects like stars actually create curvature in space itself, bending the path that light travels (a mind-bending idea that helped prove his theory of relativity).

You can also use curvature to describe the curved shape of things like a spine (doctors check for problems with spinal curvature), a road (highways with gentle curvature are safer than ones with sharp curves), or even a graph in math class. The word helps us talk about how much and in what way something bends.