Although laymen often use the words "motor" and "engine" interchangeably, from a technical point of view, an engine uses fuel to create heat that it converts into motion, while a motor uses electricity to produce motion. Historically, an engine is technically any machine that converts energy into force, such as a catapult, according to Reference.com.
An automobile generally has one engine but several motors. Examples of motors in a car include the starter, wiper motor, fuel pump and heater fan motor. The engine burns fuel, typically gasoline, to propel the vehicle forward. As the engine turns, it also powers the generator that charges the battery, which provides the power required for the various motors in the vehicle. However, the engine remains the prime mover of the vehicle as it drives.
Wikipedia attributes the confusion between motors to the early days of the automobile. To distinguish the new internal combustion engine from the older steam engine, the name "motorcar" became popular for the vehicle.
Karl Benz created the first successful automobile. Its invention added to the interest in lightweight yet powerful engines. The gasoline, four-stroke Otto cycle engine grew to become the most successful for use in the passenger automobile. Diesel engines, offering more power, became popular for larger trucks and buses. Greater fuel efficiency has increased the popularity of the turbo diesel engine in smaller vehicles.