[StephenBatey]

USB stands for Universal Serial Bus - but you don't need to know that. It was a means of standardising the various ways that external devices were connected to computers - there used to be several diiferent (incompatible) methods.

The first version was servicable for slow devices like mice and keyboards, but inadequate for anything where faster transfers were needed - like disk drives. As an illustration, when my computer only ran USB1 and my wife's had USB2 support, file transfers were far, far faster if I connected the USB disk to her computer, shared it over the network and copied files that way.

Version 2, as stated, was 40 times faster, and disks were usuable.

Version 3 is faster still.

Naturally, later versions require hardware and driver support; version 3 even comes with a different connector.