Before revision: Thinking outside the box (also thinking out of the box or thinking beyond the box and, especially in Australia, thinking outside the square) is a metaphor that means to think differently, unconventionally, or from a new perspective.
After revision: Thinking outside the box (also thinking out of the box or thinking beyond the box and, especially in Australia, thinking outside the square) is a idiom that means to think differently, unconventionally, or from a new perspective.