An engine or motor is a machine designed to convert a form of energy into mechanical energy. The heat engine burns the fuel to produce heat and then uses it for work. The motor converts electrical energy into mechanical motion. The pneumatic motor uses compressed air; the spring motor in the wind up toy uses elastic energy. In biological systems, molecular motors, such as myosin in muscles, use chemical energy to generate force and ultimately move.

The word "engine" originates from the ancient French "engine" and the Latin "Ingenium", which is the origin of the word "ingenious". Preindustrial weapons of war, such as catapults, catapults and hammers, are known as siege engines, and knowledge of how to construct weapons is often regarded as a military secret. Gin is the abbreviation for engine. Most of the machinery invented during the industrial revolution was described as an engine steam engine, which is an obvious example. However, the original steam engine (such as Thomas Savery's) was not a mechanical engine, but a pump. In this way, the original form of fire truck was only a water pump, the engine was transported to the fire by horses.

In modern usage, the term engine usually describes equipment such as steam engines and internal combustion engines that perform mechanical work by applying torque or linear forces (usually in the form of thrust) to burn or consume fuel. The device that converts heat into motion is often referred to as an engine. Examples of torque application engines include familiar automotive gasoline and diesel engines as well as turbine shafts. Examples of engines that generate thrust include turbofans and rockets.

When the internal combustion engine was invented, the term motor was originally used to distinguish it from the steam engine, which was then widely used to power locomotives and other vehicles, such as steam rollers. The word motor comes from the Latin word moto, which means to move or keep moving. Therefore, the motor is a kind of transmission device.

Later, motors and engines became interchangeable in leisure discourse. But technically, the two words have different meanings. An engine is a device that burns or consumes fuel to change its chemical composition, while an electric motor is an electric, air or hydraulic driven device that does not change the chemical composition of its energy source. But even if rockets consume fuel, they use the term "rocket engine.".

A thermal engine can also be used as a prime mover - a component that converts changes in fluid flow or pressure into mechanical energy. Cars driven by internal combustion engines can use a variety of motors and pumps, but ultimately all of these devices are powered by the engine. Another way of looking at it is that the motor gets its power from an external source and then converts it into mechanical energy, while the engine generates power through pressure (directly from the explosive force of combustion or other chemical reactions, or the second generation of power). The effect of a force on other substances such as air, water, or steam).