conductor
A conductor is a material that lets electric charge flow through it easily, the way a wide-open pipe lets water run. Metals like copper, aluminium, gold, and silver are the everyday examples; that is why wires are made of them. A conductor answers a practical question: what should I use to carry electricity from here to there?
What makes a metal a conductor is that some of its electrons are not tied to any single atom. Instead they roam through the whole material as a sea of free electrons, also called conduction electrons. Apply even a tiny push, an electric field, and these free charges drift and a current flows. Because charge moves so freely, a conductor in electrostatic equilibrium (once the charges have settled) has no electric field inside it, and any net charge sits entirely on its outer surface.
Conductors are not only metals: salty water, the human body, and hot ionized gases (plasmas) also conduct, because they contain mobile ions or electrons. The opposite of a conductor is an insulator, in which charges are locked in place. Materials in between, which conduct only a little and can be controlled, are called semiconductors and are the heart of every computer chip.
A copper wire has so many free electrons that even a household current of a few amperes is carried while each electron drifts at well under a millimetre per second.
In a conductor, huge numbers of free electrons carry current even while drifting very slowly.
A charged conductor in equilibrium keeps all its excess charge on its surface, never in its interior, and its inside field is zero. This is why a metal car shell can protect you from a lightning strike.