The direction from an object 
to another object 
can be specified as a vector 
with tail at 
and head at 
. However, since this vector has length equal to the distance
between the objects in addition to encoding the direction from the first to the second,
it is natural to instead consider the unit vector 
(sometimes called the direction vector),
which decouples the distance from the direction.
Direction
See also
Head, Tail, Unit Vector, VectorExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Direction." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Direction.html