What is reduction and oxidation ?

Oxidation: A chemical reaction which involves addition of oxygen or removal of hydrogen or loss of electron(s) is called as oxidation.
2Mg + O2 →2MgO (addition of oxygen)
H2S + Br2 → 2HBr + S (removal of hydrogen)
Fe2+ → Fe3+ + e- (loss of electron)
Reduction: A chemical reaction which involves addition of hydrogen or removal of oxygen or gain of electron(s) is called as reduction.
2Na + H2 → 2NaH (addition of hydrogen)
CuO + H2 → Cu + H2O(removal of oxygen)
Fe3+ + e- → Fe2+ (gain of electron)