These are small 'credit card' shaped adapters that typically fit into the flat horizontal slots with a long rectangular shaped opening on the side of laptop (portable) computers. They can often be called by any of the following terms - Cardbus, ExpressCard, PC Card or PCMCIA Card (Personal Computer Memory Card International Association).

Once plugged into the side of a laptop these hardware modules can extend the physical features of your portable computer by adding improved LAN or Wireless networking facilities, among many other things, including broadband modems.