A solid figure with one face a polygon (the base) and the other faces being triangles that all share the same vertex.A line from the vertex to the center of the base polygon is called the axis of the pyramid. When this axis is perpendicular to the base, the pyramid is called a right pyramid. Otherwise, it is called an oblique pyramid.

When the base is a regular polygon and the axis is perpendicular to the base, the pyramid is called a regular pyramid, in which all the lateral faces are congruent isosceles triangles making the same angle with the base.