In science and engineering, conductors are materials that contain movable charges of electricity. When impressed with an electric potential difference, the conductor's charges begin to flow, and an electric current appears. While many conductors are metallic, there are many non-metallic conductors as well. See electrical conduction for more information on the physical mechanism for current flow in materials.
A special case of a conductor is the superconductor, a conductor that does not offer any resistance to its flowing electrons at all. Unfortunately, superconductors do not work at room temperature - the best superconductors today have a critical temperature of around 138K, or about halfway between absolute zero and room temperature.
See conductor article for other meanings of conductor.