PC Card

A computer device packaged in a small card, about the size of a credit card, in conformance with the PCMCIA standard. PC cards provide additional memory (RAM or ROM), modem and fax modem capabilities, and can even act as portable disk drives on portable (laptop) computers.

The newest version of the slot on the side of your laptop machine into which you can pop a wireless receiver or some other add-on is called an "Express Card" which comes in two flavors: a narrower one called ExpressCard/34, and a wider one called ExpressCard/54. FYI: As is the case with most kinds of technology upgrades, neither can accept cards designed for the older, PC Card standard.