Pi

Pi is an irrational number, invented a long time ago, figured out by Archimedes when he was drawing and measuring circles. It is approximately 3.14 but nobody has discovered the full equation, and it likely goes on forever. Lots of people joke about the word being a homophone for "pie", which is a pastry dish, as seen in the Songdrops song The Pi Song. It is depicted by two lines with a line on top connecting them.