"Redox" is a portmanteau of the words "reduction" and "oxidation". The term "redox" was first used in 1928.
The processes of oxidation and reduction occur simultaneously and cannot occur independently. In redox processes, the reductant transfers electrons to the oxidant. Thus, in the reaction, the reductant or reducing agent loses electrons and is oxidized, and the oxidant or oxidizing agent gains electrons and is reduced. The pair of an oxidizing and reducing agent that is involved in a particular reaction is called a redox pair. A redox couple is a reducing species and its corresponding oxidizing form, e.g., / .The oxidation alone and the reduction alone are each called a half-reaction because two half-reactions always occur together to form a whole reaction.