What is a redox reaction?

In simple and easy way,

Redox reaction is the sum of both oxidation and reduction!

Where ever both are taking place, you should call that redox reaction!

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation - reduction reaction is any chemical reaction in which the oxidation number of a molecule, atom, or ion changes by gaining or losing an electron