Pi is the ratio of the circumference of a circle to its diameter. To put it another way, it's the length of the circumference divided by the length of the diameter. Pi always works out to be the same value, no matter what size the circle is. So Pi is a Big Deal because it lets you easily measure the length of the curved line that makes up a circle. Pi = C/D, so if you know the diameter and Pi, you can calculate the circumference. IF you do the math, and divide the circumference by the diameter, you'll get 3.14159265358979323846264338327950288419716939937510..... -- where the dots represent the fact that no matter how long you keep dividing, it never comes out even and the pattern of numbers doesn't repeat. It has reportedly been calculated out to 206 billion digits!! There are charts that describe the history of Pi, which goes back to the Babylonians (2000 BC), and how accurately (or inaccurately) Pi has been calculated through the years. I'm sorry I can't make it appear in neat columns here, but you can see it neatly if you go to http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Pi_chronology.html Even though the rough value of Pi was known long before his time, the first theoretical calculation seems to have been carried out by Archimedes of Syracuse (287-212 BC). ---http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/Pi_through_the_ages.html I have altered the answer in response to comments from readers. Sorry for any mistakes.

Pi was also thought to be discovered by the chinese

Pi is the ratio of the circumference of the circle to it's diameter. Not sure who invented it, but if you're curious to find out 100,000 digits to this infamous number, go to: www.geom.uiuc.edu/~huberty/math5337/groupe/digits.html

Everyone knows Pi are round.

Well, the proof that pi is irrational is NOT a simple matter. e is a LOT easier to prove irrational. In fact, it follows directly from either of the definitions of e, either the limit of (1+1/x)^x as x approaches infinity, or the Taylor series of e^x. The proof that pi is irrational was done in 1768 by Johann Lambert. His proof was first to prove that if x is rational and not 0, then tan(x) is irrational, and since tan(pi/4)=1, if pi were rational then pi/4 would be rational and tan(pi/4) would have to be irrational, which it is not because it is 1 which is rational. Oddly enough, even though e is trivially easy (in my humble opinion, having done it from each definition of e when I was in high school myself and without help) to prove irrational, Lambert was the first to do that as well, also in 1768.

Wikipedia: The mathematical constant π is an irrational real number, approximately equal to 3.14159, which is the ratio of a circle's circumference to its diameter in Euclidean geometry. Pi is special because , no matter how many decimal places you take it to, it never repeats a number or a sequence of numbers. The numerical value of π truncated to 500 decimal places is: 3.141592653589793238462643383279502884197169399375105820974944592307816406286 208998628034825342117067982148086513282306647093844609550582231725359408128481 117450284102701938521105559644622948954930381964428810975665933446128475648233 786783165271201909145648566923460348610454326648213393607260249141273724587006 606315588174881520920962829254091715364367892590360011330530548820466521384146 951941511609433057270365759591953092186117381932611793105118548074462379962749 56735188575272489122793818301194912 The value of π has been known in some form since antiquity. As early as the 19th century BC, Babylonian mathematicians were using π = 25⁄8, which is within 0.5% of the true value. The Egyptian scribe Ahmes wrote the oldest known text to give an approximate value for π, citing a Middle Kingdom papyrus, corresponding to a value of 256 divided by 81 or 3.160. It is sometimes claimed that the Bible states that π = 3, based on a passage in 1 Kings 7:23 giving measurements for a round basin as having a 10 cubit diameter and a 30 cubit circumference. Rabbi Nehemiah explained this by the diameter being measured from outside rim to outside rim while the circumference was the inner brim; but it may suffice that the measurements are given in round numbers. Principle of Archimedes' method to approximate πArchimedes of Syracuse discovered, by considering the perimeters of 96-sided polygons inscribing a circle and inscribed by it, that π is between 223⁄71 and 22⁄7. The average of these two values is roughly 3.1419. The Chinese mathematician Liu Hui computed π to 3.141014 in AD 263 and suggested that 3.14 was a good approximation

Pi is the relationship between the area of a circle and the square of the radius of that circle. Aprox value is 3.14

Pi or π is one of the most important mathematical constants, approximately equal to 3.14159. It represents the ratio of any circle's circumference to its diameter in Euclidean geometry, which is the same as the ratio of a circle's area to the square of its radius. Many other formulas from mathematics, science, and engineering include π. It is an irrational number, which means that its decimal expansion never ends or repeats. For more information on Pi visit http://en.wikipedia.org/wiki/Pi

Consider any circle of any radius. The circumference of this circle always is little more than 3 times its diameter. And this "little more" is always one-seventh of its diameter. So the circumference is always 3+(1/7) of its diameter, which you can write as (21/7)+(1/7)=(22/7). This value, 22/7 is called as "pi".

But what is the Platonic marriage number, where the product of pi digits 3141592654 = 129,600?

It slays the natives if you can tell them that pi equals 3.1415926--which is easy to remember from the number of letters in the phrase "Yes, I want a drink; alcoholic of course."

Pi is 3.14159265358979323846 etc. thats on top of my head! Pi is 200bc years old and you know what im only 7th grade and i know that!Pi keeps going on forever it never stops! PI day is officially march 14th! PI IS THE NUMBER OF TIMES A CIRCLE'S DIAMETER WILL FIT AROUND ITS CIRCUMFERENCE!PI IS THE 16TH LETTER OF THE GREEK ALPHABET.In 1706 William Jones first gave the Greek letter "π" its current mathematical definition.All the digits of Pi can never be fully known.Three point one four one five nine two It’s been around forever - its not new It appears everywhere in here and in there Its irrational I know but its true!The 3,000,000,000th decimal digit of PI is an 8. There thats all I know about Pi ask more questions and ill answer them!

opps I learned that in 7th grade im sorry!

It doesn't have almost infinite digits. It was discovered that it has about 12 trillion decimal places, which is no where near infinity. :-)