cone! spherical! round!
NOT oval
A
cone is a
three-dimensional geometric shape that tapers smoothly from a flat, usually circular
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.
In common usage in elementary
geometry, cones are assumed to be
right circular, where
right means that the axis passes through the centre of the base (suitably defined)
at right angles to its plane, and
circular means that the base is a
circle. Contrasted with right cones are
oblique cones, in which the axis does not pass perpendicularly through the centre of the base.
[1] In general, however, the base may be any shape, and the apex may lie anywhere (though it is often assumed that the base is bounded and has nonzero
area, and that the apex lies outside the plane of the base). For example, a
pyramid is technically a cone with a
polygonal base.
