Cardbus is the name given to the peripheral devices that connect usually to laptops. They take the form of cards that can be plugged into a slot.
Cardbus is the name given to PCMCIA cards v5.0 or later and they utilise 32-bit PCMCIA cards.
Cardbus includes bus mastering and this allows the bus to communicate to the other computer devices without going through the CPU, hence increasing the speed of communication.
Note: CardBus 32-bit cards cannot be used in a 16-bit slot, but most of the new cardbus slots will allow both 32-bit and 16-bit devices.