Motorcyclists and car enthusiasts use the term airbox for what might more properly be described as an air intake chamber. Older engines drew air directly from the surroundings into each individual carburetor. Modern engines instead draw air into an airbox, which is connected by individual hoses to each carburetor.
This allows the use of one air filter instead of many, and allows the designers to exploit the properties of air to improve performance. For example, modern high-performance motorcycles have the airbox draw air from the front of the bike, so that air is forced in, rather than having to be sucked in. To the same end, designers exploit a property of air cavities known as Helmholtz Resonance.