Pi is the ratio of the distance of the circumference of a circle to the length across the circle.
The circumference ( from Latin circumferentia , meaning `` carrying around '' ) of a closed curve or circular object is the linear distance around its edge . In geometry , a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle . The number is a mathematical constant , the ratio of a circle 's circumference to its diameter , commonly approximated as 3.14159 .