Pi - or π - is a mathematical constant whose value is the ratio of any circle's circumference to its diameter in Euclidean space, it is the same value as the ratio of a circle's area to the square of its radius. It is approximately equal to 3.14159 in the usual decimal notation. Pi is one of the most important mathematical and physical constants: many formulae from mathematics, science, and engineering involve π.
It's also a number with endless decimal places. The Guinness-recognized record for remembered digits of π is held by Lu Chao, a 24-year-old graduate student from China, who recited pi to 67,890 digits!
When you get through all the technical terms, the bottom line is that Pi is a massively important number that impacts our world in ways that most of us never think of or imagine. It struck me as amazing that such a little word makes such a big difference in our lives.