A "peripheral device" is an external device that connects to a computer or other electronic device to enhance its functionality. Synonyms for "peripheral device" include "accessory," "add-on," "extension," "attachment," and "peripheral equipment." Each of these terms refers to a device that is not essential to the primary function of the computer or electronic device but serves to supplement or expand its capabilities. Some more industry-specific synonyms for peripheral device include "input/output device," "portable device," and "peripheral hardware." All of these terms are used interchangeably to refer to external devices that can be added to a primary device to enhance its performance.