Ohmic Potential:  IR Drop:

Electrochemical cells, such as metallic conductors, resist the flow of charge.  In both kinds of conduction, Ohm's law defines the effect of this resistance.  The product of the resistance R of a cell in ohms and the current, I in amperes is known as the ohmic potential or the IR drop of the cell.

We know in which while applied potention, E_applied   = E_cell, no current flows by the cell. While you gradually increase the applied potential, a small current appears in the circuit.  This current by the cell encounters resistance R resulting in a potential drop of -IR volts.  Alternatively, the applied potential must be greater than the theoretical cell potential through -IR volts.  Therefore, in the presence of a current, a cell potential must be changed through the addition of the term -IR.

E_applied = E_cell - IR

E_applied   = E_cathode   - E_anode - IR

where E_cathode   and  E_anode   = E_cell are electrode potentials  computed along with the Nernst equation.