If you want to refresh an old memory, it actually stands for "Personal Computer Memory Card International Association" but nobody knew that. And it was later called 'PC Card'... then there was the faster ExpressCard that wasn't backwards compatible.

It was fun being able to expand your computer's IO capabilities by adding on a network card, modem, USB, FireWire, etc. with these modules. It's similar to Framework's little USB-C-based modules, though those modules are just too small for a lot of circuits without a very creative design.