An arrow within the plane or within the space ist characterised by its length and its orientation. The set of all arrows with the same lenght and the same orientation represents a vector of the plane resp. the space.
Thus a vector can be seen as a class of arrows, i.e. an infinite set of equal long and equal orientated arrows. The arrows are named representives of the vector.
Each vector with the lenght of one metric unit is called unit vector.