Your computer has a number of ways to connect to external devices, but the Universal Serial Bus -- or USB, as it's usually abbreviated -- is probably the most versatile. It can be used to connect to printers, thumb drives and a variety of other external devices, or to accept input from a keyboard or mouse. Your mouse and keyboard are examples of what are called Human Interface Devices. Any device that's HID-compliant uses a universal, standard driver and won't require you to install any custom driver software.
Setting the Standard
The consortium of manufacturers responsible for the USB specification grouped devices together into several broad classes, such as communication, mass storage and audio, which shared similar data-transfer needs. As the name suggests, most devices in the HID class directly transfer human input to the computer. These include game controllers and trackballs, as well as less-obvious choices such as sliders, knobs and switches on the computer's case. A few, such as steering wheels and flight yolks with tactile feedback, also communicate from the computer to the end user.