In physics, "displacement" is defined as the change in position of an object, including how far the object travels and in what direction. If an object moves around but returns to its original position, the object will move though a distance but will not have a displacement.
The concept of displacement is easily visualized by a person traveling between locations. If the person moves 3 miles west but then moves 3 miles east, although he travels 6 miles in total, his displacement is zero, since he returns to his original location. This is because, unlike displacement, distance is only concerned with the amount of travel, not the direction.