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A lemon is a car, often new, that is found to be defective only after it has been bought. Any vehicle with numerous, severe issues can be termed a "lemon," and, by extension, any product with flaws too great or severe to serve its purpose can be described as a "lemon."
The use of the word 'lemon' to describe a highly flawed item predates its use in describing cars, and can be traced back to the beginning of the 20th century as a British and American slang. Julian Koenig used the term to refer to a defective model in Volkswagen's 1950s Think Small advertising campaign.
Economist George Akerlof has also been credited with coining the term in his 1970 paper "The Market for Lemons: Quality Uncertainty and the Market Mechanism." Akerlof identified the severe lemon problems that may afflict markets characterized by asymmetrical information. A study of rejections of important economic papers noted that before Akerlof's paper was accepted, The first lemon law was proposed in California in 1980.
New vehicles 
New vehicles may contain hidden mechanical flaws or defects in workmanship, caused by design flaws or by an error during the automotive factory build process. These errors can range from parts being installed incorrectly to a tool that was used to build the car not being removed or a batch of materials with structural or chemical flaws.
Consumer protection legislation typically labels vehicles as "lemons" if the same problem recurs despite multiple repair attempts (such as three times in a row over a short period, where previous attempts have not fixed the problem) or where defects have caused a new vehicle to be out of service for a prolonged period (typically thirty days or longer) for repairs.
Lemon laws primarily serve to force manufacturers to buy back defective vehicles or exchange them. Depending on the jurisdiction, a process similar to vehicle title branding may also be used to warn subsequent purchasers of the history of a problem vehicle. While this portion of a vehicle's history is usually not retained with the title when exporting it to another jurisdiction, at least one jurisdiction (California) has started compelling manufacturers to brand the titles of any previously reacquired vehicles that they import into or out of the jurisdiction.
Used vehicles 
While used cars may be plagued with the same problems that beset new vehicles, used vehicles may also have been abused, improperly maintained or poorly repaired, been unprofessionally rebuilt after a collision or tampered with in some manner to conceal high mileage, mechanical defects, corrosion or other damage.
One form of lemon is called a cut and shut or clipping, a form of body collision "repair" based on buying a wrecked car and sawing off the wrecked section to replace it with a matching section from another (similar) car. If improperly repaired these vehicles may be inherently dangerous; at high speeds, or in an accident, the car may come apart due to the weaknesses of the welds or pins connecting the two segments of the vehicle or mismatches of segments. In the UK cut and shut cars are treated like any car that has had major repair work resulting in what is essentially a new car. They must first be inspected for road-worthiness, be assigned a new registration number and pass the standard MOT test. If this is successful they will be given a "Q" registration, meaning they are a kit, or composite car and not an original unit from the manufacturer.  In some states of the USA, the sale of cut and shut vehicles is illegal. Cars created using two or more large sections of previous ones are sometimes called "zipper cars".
Improperly repaired collision-damage vehicles also carry the risk of unibody problems. Unlike heavy trucks and lorries, most passenger cars manufactured since 1987 employ unibody construction instead of a separate body and frame. This saves weight, but the unibody is prone to bend (it is designed to do so in an impact, to absorb part of the energy of the shock) or suffer damage in severe collisions, causing the vehicle not to handle correctly or causing other mechanical parts to wear prematurely if the damaged unibody vehicle is driven after an accident.
Today, there are vehicle history services that can help a prospective used car buyer by providing a "history report" based on the vehicle's identification number(VIN). These reports will indicate items of public record, such as vehicle title branding, lemon law buybacks and recalls. They may indicate minor/moderate collision damage or improper vehicle maintenance. An attempt to identify vehicles which have been previously owned by hire car rental agencies, police and emergency services or taxi fleets is also made. However, consumers should research vehicles carefully, as these reporting services only report the information to which they have access.
Manufacturers have been known to "hide" lemon law buybacks from these reporting services through such unscrupulous methods as holding the buyback vehicle in a dealer's inventory for a short period of time, then funneling it through routine inventory (so-called "dealer only") auctions where the buyback vehicle re-enters the used market as a seemingly legitimate vehicle. While history reports can provide useful information and highlight trouble areas, consumers are still advised to have a trusted, independent mechanic perform a pre-buy inspection on any used vehicle of which they do not personally know the history.
See also 
- 24 Hours of LeMons
- Canadian Motor Vehicle Arbitration Plan
- Decrepit car
- Lemon socialism
- Total loss
- Vehicle title branding
- The Origin of “Lemon Law” is Murky
- Online Etymology Dictionary
- Volkswagen's Lemon Ad
- George Akerlof (biography)
- California lemon law, information Web site citing to Section 1793.23(a) of California's lemon law statute, which requires title branding for imported and exported vehicles.
- "Illegal cars". Retrieved 30 September 2010.
- "CUT AND SHUT ACCIDENT HORRORS - BAN THE ‘FRANKENSTEIN’ CARS". Retrieved 30 September 2010.
- "Guidelines on how you can register kit cars and rebuilt or radically altered vehicles". Retrieved 30 September 2010.