This means that it has both direction and magnitude. It will always be positive if it is in an arbitrarily defined direction, negative if it is against this direction and 0 if the object in question returned to its initial point.
For example sake:
Suppose we arbitrarily take east to be positive:
1. John rides his bicycle 10 meters eastward and rests. At that point of resting, John's displacement is 10 meters eastward.
2. After resting, John decides to ride his bicycle 10 meters westward. If this is done, John's displacement is 0 meters: there is no change in his position.
3. John decides to ride a further 5 meters westward to greet his friend: in this case, his displacement is −5 meters. But, we know which direction is positive and a negative sign preceding the magnitude indicates a movement against our arbitrary direction, that is - 5 meters is equivalent to 5 meters westward.
