FireWire cables, also commonly referred to as IEEE 1394 cables, are a specific type of serial bus commonly used for high-speed and real-tie data transfer. It was developed all the way back in the 1980s by Apple, who was the first company to actually give it its name. Other developers of the era also offered IEEE 1394 as an interface standard, though they went by different brand names like i.LINK (in the case of Sony) and Lynx (in the case of Texas Instruments). Because Apple stuck with the standard longer than anyone else, the name "FireWire" essentially became the defacto way to refer to these cables.
FireWire Cable Types
These days, FireWire cables are still incredibly common in terms of mobile devices in particular. There was a period where it was hard to buy a digital camera that DIDN'T come with FireWire as a connection standard, though that era has given way to the rise of smartphones.
The two main types of FireWire cables to concern yourself are FireWire 400 to 800. The numbers designate the maximum speeds that these types of cables can actually achieve. FireWire 400 cables can achieve speeds of up to 400 Mbps, for example, while FireWire 800 cables can obviously achieve speeds of up to 800 Mbps.
If your smartphone, external hard drive or other mobile device has a FireWire connection with either four or six pins, this means that it meets the FireWire 400 standard and this is the type of cable you need to buy should your existing one ever need to be replaced. If your device's connection has nine pins, this means that you can unlock the true potential that only FireWire 800 cables bring to the table. Either option will be significantly faster than alternative data transfer methods, however, with standard USB being the most prominent example.