# Introduction to Pyramids

A pyramid is solid figure whose base is a polygon and whose sides meet at a common point. This common point is called the vertex or apex of the pyramid. The triangular sides are called the lateral faces. The altitude of a pyramid is the perpendicular distance from the vertex to the base. A pyramid is named according to the shape of its base. A triangular pyramid is a pyramid that has a triangular base, a squared pyramid is one with a square base, etc.

A right pyramid or a regular pyramid is a pyramid whose base is a regular polygon and whose lateral faces are congruent isosceles triangles. In a regular pyramid, the axis (the line drawn from the vertex to the center of the base) is perpendicular to the base. Thus, in a regular pyramid, the axis and the altitude are identical. In the figure, $OF$ is the altitude and it shows a regular pyramid with a square base.

The slant height of a right pyramid is a line drawn from the vertex to the center of one edge of the base. In the figure, $EF$ is a slant height. A lateral edge is a line in which two faces meet. In the figure, $DF$ is a lateral edge.