When an object moves, its position changes as a function of time. A change in position is called a displacement . The position of an object is given relative to some agreed upon reference point. It is not enough to just specify the distance from the reference point. We also have to specify the direction .
Distance is a scalar quantity, it is a number given in some units .
Position is a vector quantity. It has a magnitude as well as a direction. A unit vector is a dimensionless vector with magnitude 1. It is used to specify a direction. In text, vector quantities are usually printed in boldface type or with an arrow above the symbol.