Damned lies and statistics

Would someone who understands standard deviation please explain it to me very simply, as if they were talking to a five year old?

(Preferably without using words like "statistical representation", "graphical analysis" and "inter quartile").

I have an exam on Tuesday. And bizarrely, not doing maths for twelve years hasn't (as I'd expected) made me automatically good at it without any effort at all. I thought it might be like a sprained muscle, and if I rested my maths inability for a bit then it might get better all by itself. It didn't.

I still don't know all of my eight times table. Don't tell anyone at work.