The reaction which involves simultaneous oxidation and reduction is called an oxidation-reduction or redox reaction.
In a redox reaction, one reactant gets oxidised while the other gets reduced during a reaction.
Redox reaction = Reduction + Oxidation
In redox reaction, the reductant is oxidized by the oxidant and the oxidant is reduced by the reductant.
Example: CuO(s) + H2(g) → Cu(s) + H2O
In this reaction, oxygen is removed from copper oxide therefore it is a reduction of CuO, while hydrogen accepts oxygen to form water that means oxidation of hydrogen takes place. Thus oxidation and reduction reactions occur simultaneously.
Other examples of redox reactions:
