A conductor is a material that contains movable electrical charges. Metallic is the most familiar type of conductor. In metallic conductors, the moveable charged particles are electrons. Copper and aluminum are common metallic conductors.
Copper is the most commonly used metal used in electrical wiring, but silver is the best conductor. Silver is more expensive, though. Gold doesn’t corrode and is therefore used for high quality surface to surface contacts.
There are non-metallic conductors, too. Graphite and all plasmas are decent conductors. There are even conductive polymers. Copper wiring is often used in the electrical workings of buildings and houses. It is not uncommon for junkies and thieves with a lot of time to strip buildings of the copper wiring inside the walls and air conditioning units.
Abandoned buildings are especially vulnerable of being stripped of their copper wiring. The wire is then sold and melted. Fixing stripped walls of copper wiring is expensive and many construction sites in cities have security at night to help prevent stripping from taking place.