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. Chemical systems that are not at equilibrium may still be characterized by these quantities, but each species, each location, or each time, will have a different characteristic value.