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.