In mathematical terms, pi is the ratio of the diameter of a circle to its circumference. Rounded to two decimal places, it's 3.14. So, March 14 - the 14th day of the third month - is National Pi Day.
According to the people who research this stuff, about one in five Americans have no idea know what pi is. But most people know enough about pi to recognize that it equals a great deal.
At Blaze Pizza in Meridian, it was not your typical Tuesday, with pizzas being pushed down the line and into the oven at an alarming pace. A line of customers stretched out the door and around the corner, with some waiting an hour to get their hands on a discounted pie.
On Pi Day, a normally $8 pizza pie only costs $3.14.
"The pizza's phenomenal and it's a good price," said customer Katie Bettinger, who waited about an hour to get her Pi Day pie.
Meridian pizza parlor goes all in on Pi Day
It's the kind of day that keeps Corby, who works the oven, fast-firing the pizza for exactly 188 and a half seconds, or roughly 3.14 minutes.
Manager Rob Nickel puts all 33 of his employees on duty for Pi Day.
"Everybody's working today, nobody got this day off," he said.
Pi is known as an irrational number - but a $3 pizza seems pretty rational to those willing to wait for one. However, if you ask those at Blaze Pizza to put pi into practice, it gets a little tricky.
"I know that it starts at 3.14 and goes for a long time," said Katie. "I care because it gets me cheap pizza."
Last year when Blaze Pizza did this promotion they sold a little more than a 1,000 pizzas on Pi Day. Nationwide they sold more than 140,000 at their more than 200 restaurants.