What is metallic corrosion ? Explain it with respect to Iron corrosion

The spontaneous destruction of a metal due to its interaction with environment is called metallic corrosion corrosion of Iron is called rusting. At a particular spot of Iron, oxidation takes place, and the spot behaves as anode. anode: $2\mathrm{Fe}\to 2{\mathrm{Fe}}^{++}+4\overline{\mathrm{e}}$
The released $\overline{\mathrm{e}}$ s move to another spot of the Iron and reduce oxygen in the presence of H⁺ ions and this spot behaves as cathode
Cathode: ${\mathrm{O}}_2+4{\mathrm{H}}^{+}+4\overline{\mathrm{e}}\to 2{\mathrm{H}}_2\mathrm{O}$
overall reacⁿ =
$2\mathrm{Fe}+{\mathrm{O}}_2+4{\mathrm{H}}^{+}\to 2{\mathrm{Fe}}^{++}+2{\mathrm{H}}_2\mathrm{O}$
Ferrous (Fe⁺⁺) ions are further oxidized to ferric (Fe⁺⁺⁺) ions by oxygen which come out as rust in the form of hydrated ferric oxide (Fe₂O₃ .xH₂O)