1. The process of burning a fuel with oxygen from the air to release energy, producing steam and carbon dioxide as byproducts: When a match is struck, energy is released by the process of combustion.

Unless things burn completely, toxic exhaust gases, such as carbon monoxide and other forms of pollution, are also produced.

2. An act of burning and a chemical reaction (oxidation) to produce heat, work, light, etc.. There are two main products of combustion, water vapor and carbon dioxide.