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.
