Drifting is a technique where the driver will intentionally oversteer the car to lose traction in the rear wheels or even all the tired, while maintaining control and driving the car through the entirety of the corner. It occurs when the front wheels are pointing in the opposite direction to the corner as the rear slip angle is greater than the front slip angle. The slip angle is when angle between a rolling wheel's direction ofd travel and the direction towards where it is pointing. This is also known as opposite lock or counter steering.
Drifting has become a competitive sports, first popular in Japan in the 70s and expanding worldwide ever since. The technique has become more popular as people have become more aware of it due to exposure in the media in films such as The Taste and the Furious: Tokyo Drift, Initial D (which is a Japanese Anime series) and even in the 2006 Disney Pixar movie Cars during the race in the Desert. There also have been multiple computer games that have heavily featured the driving technique from as early as Sega Rally and Ridge Racer to more modern games such as Gran Turismo and Forza Motorsport. It heavily features in the Need for Speed franchise and the Juiced franchise. One could also argue that the power sliding technique in the Mario Kart games is also a form of drifting.
Competitions are not so much just races between competitors, but also a judgement of their technique. Drivers are awarded for driving line, angle, speed, style and show factor which can include factors such as smoke, risky manoeuvres such as driving close to walls or designated clipping points and also the crowd's reaction. Judging usually only takes part on a very small section of the circuit on a series of interlocking corners that provide good viewing, and the rest of the track is almost irrelevant except for maintaining tire temperatures and setting up the vehicle for the first judged corner.
Cars set up for drifting are more often than not light weight rear wheel drive coupes and sedans operating on a large range of different power levels. Occasionally, four wheel drive vehicles have been modified so that they become rear wheel drive - a good example of this is the Suburu WRX which has featured in several drifting competitions. There are a lot of Japanese imported cars used in drifting competitions, although the trend these days is to use vehicles local to the country of the competition or the competitor.
To perform a drift you have to combine two primary driving techniques; clutching and braking. A common technique is when approaching a corner the driver will push in the clutch and drop to second gear before revving the engine to around 4500 rpm. As the clutch is then released there is a large surge in power to the wheels as the engine is spinning too quickly which makes the back wheels spin quickly and lose traction, swinging the back of the car into the turn. The driver can also use the emergency brake (also known as the handbrake) when entering a turn which causes the back wheels to lock up and lose traction. This can actually also be performed in a front wheel drive. To control the drift without spinning the car is the hardest part of the manoeuvre and requires a lot of practice to pull off using a combination of throttle and steering motions.