Many people across the world are celebrating Pi Day on Friday. Restaurants are celebrating the day with deals on a slice of pie or pizza. See the biggest deals below.

To some people, Pi Day is about mathematics. To others, it’s an excuse to eat pizza. Either way, there will be celebrations on Friday, March 14. Pi is the ratio of a circle’s circumference to its diameter, named after a Greek letter. It’s a constant number with an infinite number of digits, as explained by the U.S. Census Bureau.

It's National Pi Day, so treat yourself to some pie — pizza, dessert or both, whatever your heart desires! That first "Pi" isn't a typo and differs from the tasty "pie" we eat, though we could easily draw some geometric similarities between the two.