A cylinder is a three-dimensional geometric shape that has two parallel congruent bases, which are usually in the shape of a circle, and a curved surface connecting the bases. The distance between the two bases is the height of the cylinder. The formula for the volume of a cylinder is V = πr2h, where r is the radius of the base and h is the height of the cylinder. The formula for the surface area of a cylinder is A = 2πr2 + 2πrh, where r is the radius of the base and h is the height of the cylinder.