In terms of electron transfer, oxidation is defined as losing of electrons while reduction is the gaining of electrons for when an element gives away negatively charged particles in a redox reaction, it is being oxidized (oxidation) and if it accepts, it is being reduced (reduction).
Oxidation can never happen without being accompanied by reduction. Another element in the reaction should be reduced an equal amount in order to have the element oxidized. If an element (in electron transfer) loses electrons (oxidation) there should be another element being reduced (reduction) to take those negatively charged particles (electrons).
