Design Thinking is using the tools of design to find and implement beautiful solutions to wicked problems. As a former graphic designer, I often would look at a project from multiple angels simultaneously. I still do. It is wholistic approach to problem solving and allows for the combination of old with new, proven and unproven, deep and wide. It does not depend on "thinking outside of the box" because Design Thinkers often ask, "What box is this? Why are we in it? And who put us here?"
In an old post, Paula Thornton defines the basics -- the table stakes -- of Design Thinking. It is worth the read and the reminder.