pi / pie / pye are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
pi: (noun) the ratio of the circumference to the diameter of a circle; approximately equal to 3.14159265358979323846.... (noun) the 16th letter of the Greek alphabet.
pie: (noun) dish baked in pastry-lined pan often with a pastry top.
pye: NA
pi: p·AY
pie: p·AY
pye: p·AY
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)