A USB switch is a device that allows multiple computers to share a single USB device, such as a printer, scanner, or external hard drive. By connecting the USB switch to the computers and the USB device, users can easily switch between different systems without needing to unplug and replug cables. These switches typically come with buttons or a software interface to select which computer can access the shared USB device at any given time. This functionality is particularly useful in office environments or homes where multiple users need to access the same peripherals efficiently.