A conductor is a material that allows the flow of electric current, due to the presence of mobile charges (often in the form of free electrons). When a potential difference (voltage) is applied across a conductor, these mobile charges move from higher potential to lower potential, constituting an electric current. Metals are generally good conductors of electricity, as they have a large number of free electrons. Other materials, such as electrolytes (salt solutions or molten salts) and semiconductors, can also be conductors. Superconductors are materials that exhibit zero electrical resistance at very low temperatures.

Insulator

An insulator is a material that does not allow the flow of electric current, due to the absence of mobile charges. When a potential difference is applied across an insulator, no significant electric current flows through the material. Insulators are often used to separate conductors and to prevent the flow of current where it is not desired. Common insulators include rubber, plastic, glass, and ceramics.