Pi is a dimensionless number that never ends and never repeats. The ratio of the circumference of a circle to the diameter. No matter what the size, divide the circumference (the distance around the circle) by the diameter and you will always get exactly the same number.
First 100 digits - \(3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679...\)
Abbreviated as \(\pi\)