Ohm is the unit used to measure resistance to the passage of an electric current.
All materials resist the flow of electric current.
But some materials offer more resistance than others. Materials that offer little resistance are called conductors. Materials that offer great resistance are called insulators. The resistance of a conductor depends on its dimensions and its temperature as well as on the material from which the conductor is made. For example, the resistance of a wire increases as its length increases or as its diameter decreases.