Ohm’s law gives a relationship between current (I) and potential difference (V).

According to ohm’s law: At constant temperature, the current flowing through a conductor is directly proportional to the potential difference across its ends.

If I is the current flowing through a conductor and V is the p.d. across its ends, then according to the ohm’s law:

I ∝ V

or, V ∝ I

or, V = RI

or R = V/I

where, R is a constant called "resistance" of the conductor.

The unit of resistance is ohm.

If V = 1 volt and I = 1 amp, then R = 1/1 = 1 ohm

Thus, 1 ohm is the resistance of a conductor such that when a potential difference of 1 volt is applied to ends, a current of 1 amp flows through it.