The reactions in which oxidation and reduction are taking place at the same time are called redox reactions.

For examples:

In the above example, Fe₂O₃ is reduced to Fe by losing oxygen atoms.

Thus, Fe undergoes reduction.

CO is oxidized to CO₂ by gaining oxygen atom. Thus, C undergoes oxidation.

CuO + H₂→ Cu + H₂O

In the given reaction, CuO is reduced to Cu by losing oxygen. Thus, Cu undergoes reduction.

H₂ is oxidized to H₂O by gaining oxygen atom. Thus, H₂ undergoes oxidation.