Christmas Pi

So Daniel, my four-year-old, picked out a cool gift for me this Christmas: a Pi T-shirt.

Now, I like the shirt, and I like that he knew I would enjoy it. But most of all, I loved when he sat down with me and explained what the shirt meant. The conversation went something like this:

ME: Daniel, I really like the shirt you got me for Christmas. Thank you!
DANIEL: Yeah. That's pi.
ME: I know. It's really cool.
DANIEL: Pi is a number made up of a whole bunch of numbers.
ME: Yes, it's a number between three and four. Do you know what it means?
DANIEL: It's a number that tells you how big a circle is.

Now, I don't know about you, but... I think that's an incredible answer to "what is pi?" for someone who is four.