What most people call a true

cone - a two-dimensional

shape (usually a

rectangle in this case) extended upwards and tapered to a point. In the mathematical sense, it refers specifically to a cone with a square as its base, though all you

perverts often refer to "triangular pyramids" and the like. At least the

Egyptians were nice enough to keep the

base as accurate of a

square as possible.

On a related note, a strict pyramid is not a platonic solid, whereas an equilateral triangular cone (i.e. tetrahedron) *can* be (although it requires that the base be equilateral and its extruding line segment be orthogonal to the base and with a length exactly right to make the sides also equilateral - not so easy to compute as one might think).