Pertains to any engine in which the heat or pressure necessary to produce power is developed in the engine cylinder by the combustion of a fuel.

the combustion of fuel inside a cylinder (as in an internal-combustion engine)

Burns inside. A type of engine that creates power by burning a fuel internally. Unlike externally as with a steam engine. Most cars on the road today use internal combustion engines, including those using petrol and diesel fuels.

Term used to describe heat engines in which the working fluid of the engine is mixed with and comes into direct contact with the heat source and then exhausted after the expansion process.

Power is caused by the combustion of fuel within this type of engine, such as a gasoline engine where the fuel is burned in a cylinder, powering the engine. A steam engine is not an internal combustion engine because the steam that powers it as been caused by burning fuel in a boiler and not the engine.