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 Resource. https://mathworld.wolfram.com/Direction.html