Pi is a constant (approximately equal to 3. 14 15926), indicating the ratio of circumference to diameter. It is an irrational number, that is, an infinite cycle decimal. But in daily life, pi is usually calculated as 3. 14. Even if engineers or physicists want to calculate more accurately, they only take the value to about 20 decimal places.

π(pai) is the 6th Greek letter/kloc-0, which has nothing to do with pi, but the great mathematician Euler began to express pi in 1736. Because he is a great mathematician, people have followed suit and expressed pi. But π can be used to represent something other than pi, which can also be seen in statistics.