Oxidation: A chemical process in which an atom, ion, or molecule loses electrons. When a substance undergoes oxidation, it becomes more positively charged or less negatively charged. The substance that causes another to be oxidized by accepting its electrons is called an oxidizing agent or electron acceptor. Oxidation is a crucial part of redox reactions.
Example: In the reaction where iron (Fe) rusts, iron loses electrons to oxygen, becoming oxidized to form iron oxide (rust).