The symbol used by mathematicians to represent the ratio of a circle's circumference to its diameter is the lowercase Greek letter π, sometimes spelled out as pi, and derived from the first letter of the Greek word perimetros, meaning circumference.
Pi (π) Definition: Pi is a number - approximately 3.142. It is the circumference of any circle divided by its diameter. The number Pi, denoted by the Greek letter π - pronounced 'pie', is one of the most common constants in all of mathematics. It is the circumference of any circle, divided by its diameter.
In geometry, a pyramid is a polyhedron formed by connecting a polygonal base and a point, called the apex. Each base edge and apex form a triangle, called a lateral face. It is a conic solid with polygonal base. A pyramid with an n-sided base has n + 1 vertices, n + 1 faces, and 2n edges.