Pyramid:

Such pyramid is a polyhedraon containing one base and a number of isosceles triangles like faces meeting at a point named as the vertex or apex. Therefore the line joining the centre of the base and the apex is named as the axis of the solid.

A regular and right pyramid has its axis perpendicular to base and its faces are all equivalent isosceles triangles. Hence according to the shape of the base the pyramid may be triangular pyramid in diagram (a), square pyramid in diagram (b), pentagonal pyramid in diagram (c) or hexagonal in diagram (d).