Well, Shiloh guessed Pi day. However I did have one inquiry from someone so here goes.
The reduced (greatly reduced!) decimal version of Pi is 3.14. Therefore, March 14 is Pi day... 3/14
Some friends of ours form church celebrate by making a Pi (This year it was rhubarb, which is actually VERY good) and their kids write the decimal equation of Pi down the middle of the road as far as they can. (Did I say that right? :)
Anyway, that is what it is!!