Redox reactions involve changes in oxidation states due to transfer of electrons from one molecule or atom to another. They consist of two half-reactions - oxidation (loss of electrons) and reduction (gain of electrons).
This refers to a process in which a substance loses electrons during a chemical reaction.
Reduction: This refers to a process in which a substance gains electrons during a chemical reaction.
A substance that causes another substance to be oxidized by accepting its electrons. It's reduced in the process.