Reduction

The chemist defines reduction as the transfer of atoms from a substance, ion or molecule. If, for example, an iron nail is placed in a copper sulphate solution, a reddish-brown coating of metallic copper forms on the nail because the iron atoms release electrons to the copper ions. The copper is reduced (the iron oxidizes). Thus reduction is the release of oxygen or the absorption of hydrogen, in an electrochemical sense the absorption of electrons.