Combustion means "the act of burning," like the combustion of fallen leaves that, if not extinguished immediately, can result in a forest fire.
Combustion derives from the Latin word comburere, which means "to burn up." Matches, kindling, paper, and lighter fluid can be tools for combustion. In chemistry terms, combustion is any process in which a substance combines with oxygen to produce heat and light. Cars run because their engines use combustion to get the cylinders to fire.