Pi ( written as the Geek letter π) is a universal constant found by dividing the circumference of a circle by it's diameter. So if you measure the diameter of a circle you can calculate it's circumference by multiplying by π.
Circumference = π * diameter.
It's value to the nearest hundredth is 3.14 but its actual value is a decimal number that goes on without bounds. That is in Maths it is irrational and can't be written accurately as a fraction.
Pi is a number that is approximated by 3.14, or 22/7. It is the ratio of the circumference to the diameter of any circle. This ratio can be rearranged to find circumference of a circle by multiplying pi times diameter.
