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.
What the attached image says that if two solids with equal heights and base areas are cut by any parallel plane to their bases then sections of equal area (volume) would be produced in them
