Define resistivity of a material.

(N/A) The resistivity of a material is defined as the resistance offered by a conductor of that material having a unit length $(1 \ m)$ and a unit cross-sectional area $(1 \ m^2)$.
Mathematically,it is expressed as $\rho = \frac{RA}{l}$,where $R$ is the resistance,$A$ is the cross-sectional area,and $l$ is the length of the conductor.
Its $SI$ unit is $\Omega \cdot m$ (ohm-meter).