Definition of

Pi

Pi

The ratio of a circle's circumference to its diameter

In other words: all the way around a circle divided by all the way across it.

The symbol is π

No matter how large or small the circle, its circumference is always π times its diameter.

π = 3.14159265358979323846... (the digits go on forever without repeating)

A rough approximation is 22/7 (=3.1428571...), but that is not accurate.