Firewire is an interface developped by Apple Computer, tried to compete to USB, claimed to have 500Mb/s (similar with USB2.0), more stable than USB, mostly be used to transfer digital video. But it needs more Power, so most firewire products must have AC power adapter. If you have a product which has firewire interface, and want to connect to a PC, just buy a firewire card, mount into the PCI slot of the PC.
Firewire standard is also called IEEE 1394.