Some terrific responses...surprisingly, no one has mentioned education yet...
We have five classes signed up as judges already! I think our student judges may be more towards late middle-school / high-school aged.
I have used this quote for years to explain engineering to students, but I believe it is originally attributed to Arthur Wellington in his book, The Economic Theory of the Location of Railroads: "It would be well if engineering were less generally thought and even defined as the art of constructing. In a certain important sense it is rather the art of not constructing; or to define it rudely but not inaptly, it is the art of doing that well one dollar, which any bungler can do with two after a fashion."
While a lot of the other entries are funny and/or descriptive, so far the one above from SarahCurry is the only one that is both succinct and understandable for an 11 year old.
In a way, I'm slightly disappointed. Engineers are supposed to be good at reading and understanding specifications, especially a not too complicated one!! ;-)
To Quote Freeman Dyson:
"A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering."