Most spark plugs contain a copper core for increased conductivity, improved heat control and improved resistance to fouling.
"Copper spark plugs" is a term mistakenly used for a standard or traditional plug. Due to its soft nature and low melting point, using copper as an outer material would result in a plug that only lasted minutes.
A standard spark plug uses a nickel-alloy outer material fused to a copper core. Some plugs also include a coating or pad of precious metals to extend plug life. As a general rule of thumb, all spark plugs utilize a copper core, but copper is not used as an electrode material.