USB stands for Universal Serial Bus, and is a hardware port that allows a pc to connect up to 127 peripheral devices, such as mice, modems, and keyboards. USB has become a industry standard since 1996 with the advent of plug and play with the Windows 95 operating system. However it was with iMac rather than Windows that USB became widespread. USB was developed as a replacement to serial and parallel ports, because it is more reliable and faster.

USB home page - http://www.usb.org/