Redox, consists of two parts RED + OX, the RED part stands for reduction, whilst the OX part stands for oxidation which occur simultaneously within a redox reaction.
In terms of electrons, these can be defined as:
Oxidation: A loss in electrons from a species
Reduction: A gain in electrons in a species
and can be remebered by:
During a reaction, different species are responsible for the oxidation and reduction on other species. These are called oxidation and reduction agents and can be defined as:
Oxidation agents: A species which accepts electrons from another species (electron accepters).These are reduced themselves.
Reduction agents: A species which donates electrons from another species (electron donors). These are oxidised themselves.
These can be identified by looking at the oxidation states of the species:
Oxidation state: The number of electrons lost or gained by an atom in a compound which is given as a charge.