Conductor

An electric conductor is a material that allows electric charge to flow through it.  Metals such as copper, aluminum, silver, and gold are good conductors of electricity because they have a large number of free electrons that can move easily through the material.  In contrast, insulators such as rubber, plastic, and glass do not allow the flow of electric charge because they have very few free electrons.  Semiconductors, such as silicon and germanium, have intermediate conductivity and are widely used in electronics.