What does pi stand for?
pi is the sixteenth letter of the Greek alphabet (?, ?). There are other words that have the abbreviation PI. You can get their meanings at http://acronyms.thefreedictionary.com/PI.
pi in math means 3.14 or 22/7 about.
Pi is the number of times a diameter fits around its own circle. It's the circumference/diameter=3.1415......