What do you mean by resistance and also give SI unit

Solution

Resistance: It is a property of a conductor by virtue of which it opposes the flow of current through it. It is equal to the ratio of the potential difference applied across its ends and the current flowing through it.
mathematically,
Resistance = Potential difference/Current 
$or R = \frac{V}{I}$
and it's  S.I. unit is ohm