Oxidation can be defined in several different ways. The simplest and most rigorous of these is "the loss of electrons from an atom, compound or molecule." In general use, the term is generally applied to a chemical reaction of a substance with oxygen (O2) or an oxygen-containing material which adds oxygen atom(s) to the compound being oxidized. Either way, you can not create energy from nothing. Whenever something is oxidized, something else must undergo the opposite (loss of electrons), reduction. A species that causes oxidation is called an oxidant, oxidizer, or oxidizing agent. A species that causes reduction is called a reductant or reducing agent.