It's a bit of math pun for hardcore math students and nerds.
Basically, Pi Day is based off the fact that Pi is roughly equal to 3.14 ... So, seeing as how today is March 14th (hence, 3/14), today is thus dubbed "Pi Day."
akai-pyon wrote:@Drake: Alice walked up to Tekno. X3
I thought you would like to know.
@Nanase: Nothing much has happened, haha. Kaisuke's still waiting for a reply.