Explain the term resistance. Give its $SI$ unit of measurement.

The word resistance means resist or opposition that a conductor offers to the flow of charges through it. When a potential difference is applied across the conductor, the free electrons get accelerated. These moving electrons collide with other electrons and atoms due to which the electrons are slowed down. In other words, the motion of the electrons is opposed. This opposition is called resistance of the conductor. Resistance is measured in $\operatorname{ohm}(\Omega)$.