What does it mean to be the fastest car in the world? You could ask the team behind the Bugatti Veyron Super Sport, the car that held the Guinness Book record from 2010 until the title was taken away in early 2013, and returned within days. The Guinness decision-makers were hung up on a rule that could have disqualified the Veyron because the specific car used to set the record had a deactivated speed limiter, which altered the car's straight-off-the-showroom-floor status. In the end, they decided, it didn't matter. Or maybe you can ask the engineers behind the Hennessey Venom GT (the car responsible for briefly dethroning the Bugatti) what it meant to be the "fastest" if even for a short period of time. And in the eyes of some (though not the shot-callers at Guinness) the Venom GT reigns anyway.
As you'll see, the rules are almost everything, and even the fastest cars in the world can get caught up on little details, no matter what the speedometer says. That's why the Guinness Book of World Records has an official certification process for cars attempting to claim the title. Most people turn to the book as the authority on this matter, but in some cases, the rankings are open to debate. And, what if a car has the chops to make it on the list, but hasn't been certified by the Guinness Book? Such a situation can spur even more debate.
Every list has its own criteria, and even though we aren't the Guinness Book of World Records, we do need to mention some of our own. First, only street-legal production cars qualify. That's a pretty common rule for this type of list, and, to put it simply, that means modified cars or one-offs don't count. Theoretically, this ensures a level playing field because we're talking about cars that have to be designed so that anyone could buy one and legally drive it anywhere. (Obviously, obtaining the money to do so is another issue entirely.) In the case of a tie for the same top speed, the quicker one, the one with the faster 0 to 60-mile-per-hour (96.6-kilometer-per-hour) acceleration time, takes the honor (even though that's more along the lines of the "quickest car," which is another battle entirely).
That said, if you ever get the chance to ride in -- or even see -- one of these beauties in person, you probably won't care about which one is technically the fastest, or why. And nor should you.