Original: The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the six-stroke piston engine and the Wankel rotary engine.
Simplified: Most road vehicles use the internal combustion engine today, and most of those use the four-stroke engine. Another type of internal combustion engine is the Wankel engine.