A peripheral device is any external hardware that connects to a computer to add functionality. Common examples include printers, keyboards, mice, and scanners. These devices allow users to interact with the computer and perform various tasks, such as inputting data or producing physical copies of documents. Peripheral devices can be classified into two main categories: input devices and output devices. Input devices, like keyboards and mice, allow users to enter data, while output devices, such as printers and monitors, display or produce results. Some devices, like external hard drives, can serve both purposes by storing and retrieving data.