An input device is a hardware component of a computer system that is used to input data and commands into the computer. It allows the user to communicate with the computer and provide instructions for processing data. 

Some common examples of input devices include keyboards, mice, scanners, digital cameras, microphones, and touchscreens.

An output device is a hardware component of a computer system that is used to display or produce the results of the computer's processing. It takes data from the computer and converts it into a human-readable or perceivable form, such as text, images, sound, or video.

Some common examples of output devices include monitors, printers, speakers, headphones, projectors, and haptic feedback devices.