Fun facts:

• π got his own day; it’s called “National Pi Day” (14th March); so chosen because it's March 14, or 3-14, of course.
• π is known to be an irrational number it means that the digits never end or repeat in any known way.
• The most decimal places of π memorised is 70,000, and was achieved by Rajveer Meena (India) at the VIT University, Vellore, India, on 21 March 2015.
• In the Greek alphabet, π (piwas) is the sixteenth letter. In the English alphabet, p is also the sixteenth letter
  
  
  

What is π?

π is a name given to the ratio of the circumference of a circle to the diameter. That means, for any circle, you can divide the circumference (the distance around the circle) by the diameter and always get exactly the same number. It doesn't matter how big or small the circle is. π remains the same.

Why is π important for the humanity?

Who uses or cares about Π, unless you're channeling your inner Archimedes?
Well, it turns out we see Π being used in business and everyday life all the time. Whether it's the pipes running beneath your feet or the power lines humming overhead, Π is a slice of making it all work.
π seems to crop up everywhere, even in places that have no ostensible connection to circles.
The number crops up in the natural world. It appears everywhere there's a circle, of course, such as the disk of the sun, the spiral of the DNA double helix, the pupil of the eye, the concentric rings that travel outward from splashes in ponds.

Without π there would be no:

Road Trips

On the most fundamental level, π enables us to accurately calculate — and create — circles. So imagine if your car’s wheels were each a little different, each one just slightly off-center. Not only would you spend thousands at the mechanic; you’d also have a less comfy ride. We’re betting that commute down to Silicon Valley looks a lot less tempting...

Shortcuts

According to “Dr. Math” (whom we trust, because we found him on the internet), π plays an essential role in calculating air travel time and distance. Why? “When planes fly great distances, they are actually flying on an arc of a circle,” Dr. Math explains — because, you know, the Earth is round. No more jetting off to Fiji at a moment’s notice: in a world without π, you’re riding mules.

Game of Thrones, Prison Break, Breaking Bad…

That’s right: you need π to watch TV. Engineers use π to calculate and optimize sound waves, so without π, you’d probably miss the subtlety in those awkward silences between the Underwoods. Also: no radio, and maybe no telephones. Maybe our voices would become vestigial — who knows?

Froot Loops, bubbles, basketballs…

This video gives a possibly unfounded, but kind of funny, interpretation of the world without π — or, more accurately, a world without round stuff.

Pi Day

Not to go all meta on you, but without π, there wouldn’t be a Pi Day!

sources: 1, 2, 3, 4, 5, 6,7