The resistance is known as the property of substance by virtue of which it opposes the flow of current through it.
For a conductor of resistivity having a length of a conductor= l
and Area of a crosssection of conductor= A
Then the resistance of a conductor is given as
Its S.I unit is or ohm
Its Dimensions is
Resistivity or Specific Resistance
If l=1 m and A= 1 m^2
So Resistivity is numerically equal to the resistance of a substance having a unit area of cross-section and unit length.
If m is the mass, n is the number of electrons per unit volume, e is the charge of the electron and is the relaxation time
Its S.I Unit is Ohm.m