Or, “Universal Serial Bus.” A “bus” in this context means a conveyor of digital information, and “serial” means that many different devices peripheral to the microprocessor of the main computer – actually, up to 127 of them – can be daisy-chained together to plug into a single port on the computer.
USB ports transfer data at one of three rates. The rate of 1.5 megabytes per second is used for HIDs (Human Interface Devices - such as keyboards and mice). "Full Speed" devices send data at a rate of 12 MB/second. The Hi-Speed rate, which most USB 2.0 devices support, is 480 MB/second. Even this rate of data transmission is not fast enough for high quality digital components like monitors, and therefore they connect to computers in other ways.
The majority of ID card printers carry USB ports. Most of the few “parallel interface” ID printers that do not have USB ports will allow a USB conversion cable to achieve the effects of a USB port.
The importance of this to your photo ID system is that your ID badge printer, in order to print the employee ID cards or security badges you need, itself needs to receive information from ID card software installed on your computer. It is because of USB ports found on both computers and plastic card printers that this can come to pass.