From Longman Dictionary of Contemporary Englishpipi /paɪ/ noun [uncountable] technicalHM a number that is represented by the Greek letter (π) and is equal to the distance around a circle, divided by its width
Examples from the Corpus
pi• A broken networked intelligence may be able to calculate pi to the billionth digit but not forward e-mail to a new address.• Consider a symmetric equilibrium in which the n firms in industry i all charge a price pi.• Now came the pi ce de r sistance.• One of his most popular miracles occurred one day while pi owing.Origin pi (1800-1900) From the name of the first letter of Greek periphereia “distance around a circle” 