A cylinder is a surface with a circular base, a circular top of the same size, and the curved surface formed by the vertical line segments joining them. For a cylinder with base of radius r and height h, the cylinder’s interior has volume πr2h, and the area of the curved surface equals 2πrh.
More generally, a cylinder is a surface, consisting of the points of the lines, called generators, drawn through the points of a fixed curve and parallel to a fixed line. The generators may be extended indefinitely in both directions. Compare prism.