In the earliest usages, the Greek letter π was an abbreviation of the Greek word for periphery (περιφέρεια), and was combined in ratios...

The best-known approximations to π dating before the Common Era were accurate to two decimal places; this was improved upon in Chinese...

The number π (/paɪ/) is a mathematical constant. Originally defined as the ratio of a circle's circumference to its diameter, it now has...