These are slots (mostly in laptops) which lets you add features to your computer. I've seen network cards, modems, tv tuners, etc. be available for these slots. USB ports are making these slots used less and less.

Type II PCMCIA slots are used by most PCMCIA modems.

PCI, AGP, and ISA are types of expansion bus slots. These slots allow you to attach internal peripherals such as video cards, hard drive controllers, modems, tuner cards, and other things.

expansion slots

ExpressCard (formerly NewCard)

replaced PC Card or CardBus (formerly PCMCIA) standard, circa 2004.