A peripheral device is an auxiliary device that connects to the computer and works with it to process or retrieve information from the computer.

These devices are also called external peripherals, integrated peripherals, auxiliary components, or input/output (I/O) devices.

Normally, the word peripheral refers to a device that is external to the computer, such as a scanner. However, devices that are physically inside the computer are also technically peripherals.

Peripherals add functionality to the computer, but are not part of the "main" group of components such as the CPU, motherboard, and power supply. Although they are often not directly involved in the main function of a computer, this does not mean that they are not considered necessary components.