The two terms actually have very different meanings. A spur is a smaller summit located on the slope of a mountain or a large hill. By definition, it is never as high as the main summit, and can vary in size. The most famous example of a spur is the South Summit of Mount Everest. Sometimes the term can also be used to apply to a small mountain chain that juts off of a main chain. Interlocking spurs, on the other hand, are formed when erosion causes riverbanks to move down toward a river, which cuts its way through them in a zigzag pattern. While they never touch each other, and the river still winds its way through them, the interlocking spurs appear to dovetail together in a way that resembles the teeth of a zipper.