Just in case you are not a maths person, π (pi) is used to calculate, among other things, the circumference of a circle or the volume of a cylinder. Which will be a good thing to know if, say, you are doing the maths for building a spinning wheel. Or calculating the drive ratio of your wheel, and figuring out how to change it to a ratio you want. Or calculating weight and MI of spindles from a given material for a spinning experiment. Plus - I love pie. The edible kind.
If you're now frantically looking for some way to celebrate Pi Day, you can find some more information on this website. Look under "Pi Stuff" to find amusing snippets of all sorts. Or just prepare your favourite pie recipe and celebrate pi day. (And if you need an excuse for a prolonged lunch break or very early coffee break, you can always say you need to celebrate Pi Day at the correct time - at 1.59 pm.)