Oxidation in the original sense of the word used to refer to the chemical reaction of a substance with oxygen. Even today, this term is still frequently associated with the reaction of a substance with oxygen and the formation of oxides.
In fact, oxidation is a chemical reaction in which a substance to be oxidized gives off electrons and another substance takes up electrons. This is reduced by the absorption of electrons. Oxidation is therefore always associated with a reduction. Both reactions together are regarded as partial reactions of a redox reaction.