That's the Greek letter pi, the mathematical value of which is (approximately) 3.14159265 (equal to the ratio of the circumference of a circle to the diameter).  So that's why it must have occurred to some mathematician/foodie to nominate March 14 each year as Pie Day, 3/14.  Anyhow, any day is a good day to have pie!  I reminded my Old Man, a retired scientist, about the day, and he said that next year will be an extra special Pie Day, because the equivalence is typically rounded further to 3.1416.

Thinking about goofy stuff and "pie" made me remember Goldie Hawn, as the "dumb blonde" on Laugh-In.  Someone told her about the formula for finding the area of a circle, pi  r² (pi r squared).   Said Goldie:  "No they're not!  Pie are round-----cornbread are square!"

And remember my daddy who, though he never went to college, would always say he was "a frat man".  When asked about that, he would explain that he belonged to "Eat-a bite-a pie".