The Pi symbol expresses the mathematical ratio of the circumference of a circle to its diameter and is roughly equivalent to "3.1459" or twenty-two sevenths. The symbol is a special character, based off of the Greek alphabet, and is not standard on a Mac keyboard. However, the keyboards "Option" key will enable to you efficiently insert the Pi symbol into your documents.
Hold down the "Option" key on your keyboard.
Press the letter "P" while still holding the option key.
Release both keys at the same time and the Pi symbol will appear in your document or application.