*By Casey Frye, CCNN Writer*

If you saw a bunch of people wearing shirts with the Greek letter pi (π) on Friday, that’s because it was Pi Day! Why is this symbol so popular, though, and why does it get a whole day to itself, anyway?

Mathematically, pi represents the ratio (comparison) of a circle’s circumference (outer edge) to its diameter (width). Since the circumference is 3 times bigger than the diameter, plus a little extra, that comes out to roughly 3.14, better known as pi. I say “roughly” because the numbers after the decimal actually go on forever without any sensible pattern!

It’s this infinity-like characteristic that makes pi such a popular figure in math.

There are even supercomputers that are dedicated to finding pi’s end, and so far, they are trillions of numbers deep with no end in sight. According to Numberworld.org, computers calculated about 20 trillion digits! That’s too many numbers for anyone to memorize, but it doesn’t stop them from trying. In case you’re curious, the Guinness World Record holder for most numbers memorized is Chao Lu with 67,890 digits.

There are other ways to have fun with the number as well. Many folks love to make stories out of the digits of pi in a dialect (special language) called Pilish. In this nerdy, yet awesome language, people put their math and English skills to the test by creating phrases where each successive word contains as many letters as the corresponding digit in pi. Take the following Pilish phrase for example: “Eat a fish”. Since “Eat” has 3 letters, “a” has 1 letter, and “fish” has 4 letters, it matches up with the first 3 numbers in pi – 3.14. Try it for yourself; it’s harder than it seems! I don’t know how one man actually wrote a whole novel in Pilish.

Next year’s Pi Day is going to be especially enthusiastic, because the date itself – 3/14/15 – will match the first few digits of the popular number: **3.1415**9265359…

*Featured image courtesy of Tom Blackwell on Flickr. Image of pi book courtesy of Takashi Kiso on Flickr.*