Pyramid

Pyramid, in Geometry, is a solid figure, of which the base is a plane rectilinear figure, and the sides are triangles, converging to a point at the top or 'apex.' Pyramids, like prisms, are named from the form of their bases: thus, a pyramid having a triangle for its base is a triangular pyramid, with a square base, a square pyramid, with any four-sided figure for its base, a quadrangular pyramid; or it may be pentagonal, hexagonal, &c. Pyramids may be either 'right' or 'oblique' (see PRISM). A right pyramid, with an equilateral figure for its base, has all its sloping edges equal; but this is not the case if the pyramid be oblique. The most remarkable property of the pyramid is that its volume is exactly one-third of that of a prism having the same base and vertical height; and it follows from this that all pyramids having the same base and height are equal to one another. The word (Gr. pyramis) is of Egyptian origin.