en.wikipedia.org/wiki/Pi

The number π is a mathematical constant, the ratio of a circle's circumference to
its diameter, ... The symbol used by mathematicians to represent the ratio of a
circle's circumference ...

www.angio.net/pi/whypi.html

Pi (π) is the ratio of the circumference of a circle to its diameter. ... Archimedes
used this trick with 96 sided polygons to correctly estimate Pi to about two digits ...

www.livescience.com/29197-what-is-pi.html

Apr 30, 2013 ... Pi (π), the 16th letter of the Greek alphabet, is used to represent the most widely
known mathematical constant. By definition, pi is the ratio of the ...

mathforum.org/dr.math/faq/faq.pi.html

What is Pi? Who first used Pi? How do you find it? What is it for? How many digits
is it?

www.scientificamerican.com/article/what-is-pi-and-how-did-it/

According to Petr Beckmann's A History of Pi, the Greek letter was first used for
this purpose by William Jones in 1706, probably as an abbreviation of periphery,
...

www.piday.org/learn-about-pi/

Pi is a constant number, meaning that for all circles of any size, Pi will be the
same. ... The mathematician Archimedes used polygons with many sides to ...

wonderopolis.org/wonder/what-is-pi

The Greek letter π was first used to represent pi by William Jones in 1706,
because π was an abbreviation of the Greek word for perimeter: "περίμετρος." ...

www.tulsaworld.com/business/fyibusiness/pi-common-in-everyday-life-not-just-dessert/article_d1e06850-b460-5ea6-8417-29bed2386234.html

Mar 14, 2014 ... Well, it turns out we see Pi being used in business and everyday life all the time.
Whether it's the pipes running beneath your feet or the power ...

www.mathsisfun.com/numbers/pi.html

all the way around the circle) will be Pi. Pi (the symbol is the Greek letter π) is: ...
There are many special methods used to calculate π and here is one you can try
...

lightyears.blogs.cnn.com/2012/03/13/pi-day-how-3-14-helps-find-other-planets-and-more/

Mar 13, 2012 ... iReporter Zeynep Rice made this pie to celebrate Pi Day. .... H/m that's units per
Henry per meter, where a Henry is a unit used in electronics.