A folding bicycle or folder is a type of bicycle that incorporates hinges or joints in the frame and handlebar stem that permit it to be broken down into a more compact size. As well, most folders have wheels of 20 inch (51 cm) diameter or less. Folding bikes can be taken on public transport and into apartment buildings or workplaces where conventional bicycles are not allowed. This facilitates mixed-mode commuting, because a folding bike need not be parked in the street or train station. Folding also makes it easier to transport a bicycle in an automobile.
Folding bicycles often cost more than non-folding bicycles with the same performance-related features, because they have more parts, to allow folding and to lock the frame when unfolded. This results in a more complicated design, which is more complex to manufacture; as well, there is a smaller market for this type of bike. As an alternative to folding, some bicycle models achieve similar results by separating into two or more parts for more compact storage or ease in transporting. These are sometimes grouped in the same category as folding bicycles but are also referred to as break-away, disassemble-able, or separable bicycles.
Source: Wikipedia
