A headphone jack is an interface device used to connect headphones or headsets, typically consisting of a socket and pins. It enables signal transmission through physical contact between internal spring-loaded metal contacts and the metal ring of the plug. Its core structure is categorized into three-segment (TRS) headphone jacks and four-segment (TRRS) headphone jacks. Headphone jacks play a vital role in various audio devices such as mobile phones, computers, and music players.