"Think outside the box" is the phrase every douchebag boss you've ever had has said to you at least one time. "Think Outside the Box" as a phrase itself has no meaning. It literally has no useful meaning whatsoever.
What they WANT it to mean when they say it (They being of course your superiors at every job you hated when you were younger) is for you to exercise your mind and figure out the solution to a problem.
The real meaning? "I have no idea how to answer your question, so figure it out for yourself."
1.) You: Sir, I found the account you wanted me to research, but in what way am I supposed to approach a 60 year old man with no liquid assets living on social security?
Your superior who's actually awful at his AND your job: Think outside the box!
2.) You as a 3rd grader: Dad, what's 9/3?
Your dad: 2.
You as a 6th grader: Dad, if x-10 = 15, what is x?
Your dad: 25
You as a freshman in high school: Dad, if (x-10)+5(2) = 20, what is x?
Your dad: ...Think outside the box!