If you're into racing or want a motorcycle that's built for speed, you want a sport bike. This type of motorcycle may not get the best gas mileage, and it's certainly not very comfortable to ride long distances, but if you're going to race down the track and pull out ahead of everyone else, it's the type of bike you want. These motorcycles have been optimized for speed, braking, cornering, and acceleration on paved surfaces (for racing on off-road surfaces, you want a dirt bike).
In the beginning, all motorcycles were designed about the same, and while riders definitely raced them, their bikes weren't specially designed for speed. That started changing around the 1950s. In 1969, Honda produced the CB750, the first real sport bike. It was dramatically faster and more powerful than other bikes on the market. In the 1970s, advances in braking and suspension were added to the inline four cylinder engines, creating even faster sport bikes. Today, there are even more variations, giving riders who love speed many options.
Because they're all about speed, these bikes are designed to be as aerodynamic as possible. Sitting upright as a person does on a cruiser isn't very aerodynamic, so the foot pegs were moved higher and closer to the body, while the handlebars are set a bit lower. To ride, a person more or less balances their weight on their arms and wrists, putting their center of gravity forward over the tank. Of course, this is going to tire the rider pretty quickly, which is why these bikes are not recommended for long trips.
Sports bikes today are generally separated into several different categories: lightweight (500 cc or less), middleweight (600 to 750 cc), and superbike (those of 1000 cc or more). Then there is the variation known as a naked bike, which moves the handlebars up a bit, putting the rider in a more upright position.
