A cone is a three-dimensional solid that has a circular base and a vertex that is not in the same plane as the base. The altitude of a cone is the segment from the vertex that is perpendicular to the plane of the base.

The length of the altitude is called the height of the cone. If the altitude meets the base at its center, then the cone is a right cone. In a right cone, the distance from the vertex to a point on the edge of the base is called the slant height of the cone.

If a cone is not a right cone, it is called oblique.