pe·riph·er·al / pəˈrifərəl/ • adj. of, relating to, or situated on the edge or periphery of something: the peripheral areas of Europe. ∎  of secondary or minor importance; marginal: she will see their problems as peripheral to her own. ∎  (of a device) able to be attached to and used with a computer, although not an integral part of it. ∎  Anat. near the surface of the body, with special reference to the circulation and nervous system: lymphocytes from peripheral blood.• n. Comput. a peripheral device.DERIVATIVES: pe·riph·er·al·i·ty / -ˌrifəˈralitē/ n.pe·riph·er·al·i·za·tion / pəˌrifərəliˈzāshən/ n.pe·riph·er·al·ize / -ˌīz/ v.pe·riph·er·al·ly adv.

peripheral Any device, including I/O devices and backing store, that is connected to a computer. The term originated in the mainframe era when all the computing was centralized and the input/output functions were attached around the periphery of the installation. Since the advent of smaller cheaper computers, printers, etc., the term peripheral is seldom used.