Pi

The number pi, usually written with the Greek letter π, is a constant defined as the ratio between the circumference and the diameter of a circle. This ratio is the same for all circles, which is due to the fact that all circles are similar.

Since π is an irrational number, its decimal part never repeats or terminates. However, its value is often rounded to 3.14 to make calculations easier. Alternatively, π can be approximated by 227.

Graphically, π is the number of times that the diameter of the circle fits on top of the circle.