Here's why:

* Oxidation is a chemical process where a substance loses electrons.

* When a substance reacts with oxygen, the oxygen atoms gain electrons, becoming negatively charged.

* This means the substance that reacts with oxygen loses electrons, which is the definition of oxidation.

Here are some examples:

* Rusting: Iron reacts with oxygen and water to form iron oxide, commonly known as rust.

* Burning: Combustion is a rapid reaction between a substance and oxygen, releasing heat and light.

* Respiration: Living organisms use oxygen to break down food molecules for energy, releasing carbon dioxide as a byproduct.

Note: Not all reactions with oxygen are necessarily "burning". The term "burning" implies a rapid and exothermic reaction, while oxidation can occur slowly and without producing flames.