There are many mathematical ideas joined to special symbols used to concisely portray them (once they've been understood). One is the ratio of the length of the boundary or circumference of a circle to its diameter, the line through the circle center which defines its widest crossing. That quantity is called and pronounced by the sound pi.
Finding to greater accuracy was a significant task in mathematics up to a few hundred years ago.
Adding or multiplying numbers when there is no last item ... a situation usually summarized in a shorthand way by the word infinite, leads to two special symbols. The first represents addition; it is: . The second uses a special symbol to represent multiplication: