Oxidation occurs when a chemical species looses an electron.
Reduction occurs when a chemical species gains an electron. In this reaction, iron is oxidized and hydrogen is reduced. An oxidant species promotes oxidation and a reductant promotes reduction. All of these are quantitative measures of propensity of the reaction and do not take into account the kinetics or rate at which a reaction can occur. Chemical systems that are at equilibrium are characterized by these quantities throughout the volume.