A **cone** is a three-dimensional geometric shape that tapers smoothly from a flat, round *base* to a point called the *apex* or *vertex*. More precisely, it is the solid figure bounded by a plane base and the surface (called the *lateral surface*) formed by the locus of all straight line segments joining the apex to the perimeter of the base. The term "cone" sometimes refers just to the surface of this solid figure, or just to the lateral surface.

The *axis* of a cone is the straight line (if any), passing through the apex, about which the lateral surface has a rotational symmetry.