A peripheral is a piece of equipment that is attached to a host computer without being a part of it and is instead dependent on the host. It broadens the capabilities of the host, but does not form part of the core computer architecture. Common examples of peripherals include computer printers, scanners, headphones, speakers, and webcams. Some peripheral devices can be attached directly to the computer via a cord, cable, or USB device. Others can be attached wirelessly.
It is not always clear whether or not something is a peripheral. A video capture card inside a computer case is not part of the center computer, but it is however, contained in the case. Ultimately though, it is not a significant issue.