An automobile (also motor car or simply car) is a wheeled passenger vehicle that carries its own motor. Most definitions of the term specify that automobiles are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the transport of people rather than goods. However, the term is far from precise.

As of 2002, there were 590 million passenger cars worldwide (roughly one car for every eleven people)

An antique car is generally defined as a car over 25 years of age, this being the definition used by the Antique Automobile Club of America and many other organizations worldwide. However, the legal definition for the purpose of antique vehicle registration varies widely.

The term classic car is often used synonymously with antique car, but the formal definition[citation needed] of that term has it as applying only to certain specific high-quality vehicles from the pre-World War II era.

25 years is about double the design life of modern cars and an even greater increment on those cars now 25 years old; therefore, a car that’s reached 25 is a rare survivor, and probably not economic to maintain as regular transportation.

Owning, restoring and collecting antique cars is a popular hobby worldwide.

Executive car is a British term used generally to describe an automobile larger than a large family car, but which is not a high-end or ultra luxury car, a multi-purpose vehicle or a sport utility vehicle. In official use, the term is adopted by EuroNCAP, a European organization founded to test car safety.

A front-mounted engine describes the placement of an automobile engine in front of or on the front axle.

This layout is the most traditional form and remains a popular, practical design. The engine which takes up a great deal of space is packaged in a location passengers and luggage typically would not use. The main deficit is weight distribution—the heaviest component is at one end of the vehicle. Car handling is not ideal, but usually predictable.

Biodiesel refers to a diesel-equivalent, processed fuel derived from biological sources (such as vegetable oils), which can be used in unmodified diesel-engine vehicles. It is thus distinguished from the straight vegetable oils (SVO) or waste vegetable oils (WVO) used as fuels in some diesel vehicles.

In this article’s context, biodiesel refers to alkyl esters made from the transesterification of vegetable oils or animal fats. Biodiesel is biodegradable and non-toxic, and typically produces about 60% less net carbon dioxide emissions than petroleum-based diesel, as it is itself produced from atmospheric carbon dioxide via photosynthesis in plants. Pure biodiesel is available at many gas stations in Germany.

Some vehicle manufacturers are positive about the use of biodiesel, citing lower engine wear as one of the benefits of this fuel. However, as biodiesel is a better solvent than standard diesel, it ‘cleans’ the engine, removing deposits in the fuel lines, and this may cause blockages in the fuel injectors. For this reason, car manufacturers recommend that the fuel filter is changed a few months after switching to biodiesel (this part is often replaced anyway in regular servicing). Most manufacturers release lists of the cars which will run on 100% biodiesel.

Alternative Fuel Vehicle refers to a vehicle that run on a fuel other than traditional gasoline or diesel; any method of powering an engine that does not involve petroleum. Due to a combination of heavy taxes on fuel, particularly in Europe, tightening environmental laws, particularly in California, and the possibility of further restrictions on greenhouse gas emissions, work on alternative power systems for vehicles has become a high priority for governments and vehicle manufacturers around the world.

Current research and development is largely centered on “hybrid” vehicles that use both electric power and internal combustion. The first hybrid vehicle available for sale in the United States was the Honda Insight. As of 2006, the car is still in production and achieves around 60 miles per gallon (25.5km per liter).

The internal combustion engine is an engine in which the combustion, or rapid oxidation, of gas and air occurs in a confined space called a combustion chamber. This exothermic reaction of a fuel with an oxidizer creates gases of high temperature and pressure, which are permitted to expand. The defining feature of an internal combustion engine is that useful work is performed by the expanding hot gases acting directly to cause pressure, further causing movement of the piston inside the cylinder. For example by acting on pistons, rotors, or even by pressing on and moving the entire engine itself.

This contrasts with external combustion engines, such as steam engines and Stirling engines, which use an external combustion chamber to heat a separate working fluid, which then in turn does work, for example by moving a piston.

Turbodiesel refers to any diesel engine with a turbocharger. Turbocharging is the norm rather than the exception in modern car diesel engines.

This type of engine was first introduced in a production car in May 1978 in the Mercedes 300SD (series W116, engine OM617.950), only produced for the United States. In Europe, its first application was in the Peugeot 604 in early 1979 (model year 1978).

An electric vehicle, or EV, is a vehicle with one or more electric motors for propulsion. The motion may be provided either by wheels or propellers driven by rotary motors, or in the case of tracked vehicles, by linear motors.

A hydrogen vehicle is a vehicle, such as an automobile, aircraft, or any other kind of vehicle that uses hydrogen as its primary source of power for locomotion. These vehicles generally use the hydrogen in one of two methods: combustion or fuel-cell conversion: In combustion, the hydrogen is “burned” in engines in fundamentally the same method as traditional gasoline cars. In fuel-cell conversion, the hydrogen is reacted with oxygen to produce water and electricity, the latter of which is used to power electric motors.

Hydrogen can be obtained through various thermochemical methods utilizing natural gas, coal (by a process known as coal gasification), liquefied petroleum gas, biomass (biomass gasification), or from water by electrolysis or by a process called thermolysis. A primary benefit of using pure hydrogen as a power source would be that it uses oxygen from the air to produce water vapor as exhaust. Another benefit is that, theoretically, the source of pollution created today by burning fossil fuels could be moved to centralized power plants, where the byproducts of burning fossil fuels can be better controlled. Hydrogen could also be produced from renewable energy sources with (in principle) no net carbon dioxide emissions. There are both technical and economic challenges to implementing wide-scale use of hydrogen vehicles, and the timeframe in which such challenges may be overcome is likely to be at least several decades.