Resistivity defines how high the resistance is for a material with unit dimensions. It is a constant for a given material.
For example, silver has a low resistivity, so silver wire will have a lower resistance than metals of the same dimensions and higher resistivity.
Summary
The resistance of a wire depends upon what material it is made of, as well as the dimensions of the wire. The property of the wire that determines this is the resitivity.
Equation
Can you rearrange the equation to make ρ the subject?
You need to be able to rearrange equations, here is how you manipulate this one.