Pi Day is not to be confused with Pie Day, a national holiday celebrated Jan. 23. Pi Day is celebrated each year on March 14. This year’s Pi Day was special for celebrators because this year Pi Day was March 14, 2015, and at 9:26:53. It marked the “ultimate” Pi Day as it is 3.141592653.

According to Piday.org, pi symbolizes “the circumference of a circle to its diameter.” Pi is a constant that goes on infinitely.

Pi Day originated March 14, 1988 when a physicist Larry Shaw celebrated the first Pi Day, according to a CNN article, “A number of things to know about Pi.”

People celebrate the day by making and eating pie or pizza and finding different ways to acknowledge the importance of Pi.