What is pie?

If you want to be more specific, 3.1415926535897932384626433832795028841971693993751...

It is an undefined/never-ending decimal.

A pie is a baked dish which is usually made of a pastry dough casing that covers or completely contains a filling of various sweet or savoury ingredients. OR in math terms 3.14159265359

Hi

A pie is ONLY a pastry

Pi   (without the e) is an irrational number that is approximately equal to 3.14159....