National Pi Day is recognized today in the U.S. and around the world. Here's what to know about the quirky holiday, and how to celebrate.

The calendar says it's time to dig into a popular dessert and celebrate math. So, what is the significance of pi?

Pi is a mathematical constant that represents the ratio of the circumference of a circle to its diameter. It is an irrational number, meaning it cannot be expressed as a finite decimal or fraction ...

Scientists have calculated the value of pi to one hundred trillion digits, but you don't have to be a mathematician to understand it.

What is pi? Pi can calculate the circumference of a circle by measuring the diameter — the distance straight across the circle’s middle — and multiplying that by the 3.14-plus number.

While this is roughly 3.14, Pi is actually irrational, meaning there's not a finite number of numbers when written as a decimal. Why it's better to order 1 large pizza than 2 medium pizzas ...

The theory of Pi is one of the most important in all of mathematics and today Google has dedicated its homepage doodle to the day that celebrates it.