The correct phrase is "think outside the box." It refers to creativity. It is actually a reference to an old puzzle.
The puzzle shows an square array of 3 x 3 dots, with plenty of space around the array. You are challenged to draw four straight lines, without lifting the pencil off the paper, that will go through all nine dots. The solution looks like this:
To solve the puzzle, you have to use lines that go outside the 3x3 box. Many people fail because they assume that they are required to stay inside the box, although the puzzle doesn't say so. In order to solve the problem, you have to think about going outside the box--you have to "think outside the box."
So it suggests not only creativity, but the ability not to let yourself be constrained by imaginary limits.
A famous example of thinking outside the box involved the development of the car starter motor by Charles Kettering. Engineers had calculated that an electric motor powerful enough to start a car would be impractical--it would be too big, heavy, and expensive. Kettering realized that people were assuming a constraint that didn't exist. They were assuming that the motor had to deliver power continuously, for an indefinitely long period of time, without overheating and burning itself out. He realized that the car would start within a few seconds. The motor would need to run for a few seconds. It could be heavily "overloaded" safely, because it wouldn't have time to overheat. The "box" here was the idea that the motor had to be designed to run indefinitely. He realized that wasn't true. He "thought outside the box."
Unfortunately, the phrase "thinking outside the box" became overused. It's an old, stale, management buzzword. It's now sort of a joke. In a situation comedy, to show that a boss is a fool, they may have him urge his people to "think outside the box."