A metal was an element, compound, or alloy that was a good conductor of both electricity and heat. Metals were usually malleable, ductile and shiny.
The Kiseibya were a metal-eating creature developed to be a Dalek predator. (AUDIO: Enemy of the Daleks)
Gallifreyan zinc was one of the strongest metals in the universe. (AUDIO: Pier Pressure)
Photavine steel was a metal used in Tritovore ships. When it heated up, it cooled down the interior of the ship. (TV: Planet of the Dead)