What is "axis of a pyramid"

Pyramid \Pyr"a*mid\, n. [L. pyramis, -idis, fr. Gr. ?, ?, of Egyptian origin: cf. F. pyramide.]

1. A solid body standing on a triangular, square, or polygonal base, and terminating in a point at the top; especially, a structure or edifice of this shape.

2. (Geom.) A solid figure contained by a plane rectilineal figure as base and several triangles which have a common vertex and whose bases are sides of the base.

3. pl. (Billiards) The game of pool in which the balls are placed in the form of a triangle at spot. [Eng.]

4. (Finance) a fraudulent investment scheme in which the manager promises high profits, but instead of investing the money in a genuine profit-making activity, uses the money from later investors to pay the profits to earlier investors; -- also called pyramid scheme or pyramid operation. This process inevitably collapses when insufficient new investors are available, leaving the later investors with total or near-total losses of their investments. The managers usually blame government regulations or interference for the collapse of the scheme, rather than admit fraud.

   Altitude of a pyramid (Geom.), the perpendicular distance from the vertex to the plane of the base.

   Axis of a pyramid (Geom.), a straight line drawn from the vertex to the center of the base.

   Earth pyramid. (Geol.) See Earth pillars, under Earth.

   Right pyramid (Geom.) a pyramid whose axis is perpendicular to the base.