What is it? I tried to guess and I came up with two possible meanings: 1) a surprising one (as a jack-in-the-box is) 2) a fresh, new kind of situation But of course I'm not a native speaker so I need your help. No context as I heard this term a long time ago.
Think outside the box... an expression that I find tedious because of its overuse by business boys (interestingly, I don't think I've ever heard a woman use it).
If you are trying to find a solution to a problem, and you imagine yourself and the problem as being inside an imaginary box, out-of-the-box thinking -- where you set your mind free to roam outside the box into new, uncharted territory -- is supposed to help you find a solution that hasn't been thought of before.
I am guessing here, but I would think that an out-of-the-box situation is one that requires out-of-the-box thinking.
The jack-in-the-box is a charming mental image... but it's only got a 1 in a 100 chance of being right here.