Which of the following best describes a peripheral device?

A peripheral device is best described as a device that enhances the functionality of the computing environment. These devices are not essential for the basic operation of the computer, but they provide additional features or capabilities that can improve user experience or work efficiency. For example, peripherals like printers, scanners, external storage drives, and webcams are not necessary for a computer to function but significantly extend its capabilities.

In contrast, other descriptions do not accurately capture the essence of what a peripheral device is. Essential components directly crucial to the basic functionality of a computer are actually components like the CPU, RAM, and motherboard, which are not classified as peripherals. Additionally, while some peripherals may act only as input sources (such as keyboards and mice), many peripherals also serve as output devices (like monitors and printers) or both, so they cannot be limited to just input sources. Lastly, built-in components of the motherboard—such as integrated graphics or audio—are part of the computer's core architecture and do not classify as peripheral devices.