Redox reactions: in which changes in oxidation numbers of atoms in involved species occur.
Those reactions can often be interpreted as transferences of electrons between different molecular sites or species.
An example of a redox reaction is:
2 S2O32−(aq) + I2(aq) → S4O62−(aq) + 2 I−(aq)
In which I2 is reduced to I- and S2O32- (thiosulfate anion) is oxidized to S4O62-.