"there are plenty of other infinite decimal (and infinitely useful) numbers to celebrate-Feb. 7 could have been e Day, for example, or Jan. 6, the Day of the Golden Ratio."
"π has fascinated mathematicians, engineers and other people for centuries. It is a mathematical constant that is the ratio of a circle's circumference (C) to its diameter (d); This also explains why and how this number got its name: the lowercase π was first adopted in 1706 as an abbreviation for this number because it is the first letter of the Greek for "perimeter", specifically of a circle." Introduces a video by Numberphile explaining more about the determination of π