what is resistivity?

The factor in the resistance which takes into account the nature of the material is the resistivity.
Resistivity is theresistance of a unit cube of the material measured between the opposite faces of the cube.
Resistivity depends strongly on the presence of impurities in the material.
Resistivity depends strongly on the temperature of the material.

The electrical resistance of a wire is greater for a longer wire and less for a wire of larger cross sectional area. The resistance depend on the material of which it is made and can be expressed as:

R = ρ L / A

where

R= resistance (ohm,Ω)

ρ= resistivity coefficient (ohm m, Ω m)

L= length of wire (m)

A= cross sectional area of wire (m²)

The factor in the resistance which takes into account the nature of the material is the resistivity. Since it is temperature dependent, it can be used to calculate the resistance of a wire of given geometry at different temperatures.