The audio jack is a plug for transmitting low voltage. It is often used for audio or video connections and to connect electric or electro-acoustic ukuleles to amplifiers or headphones.. The plug contains a contact spring which can wear out with time. Thus, plugs can get loose (slack joint), and transmission quality can decline.

For audio devices and musical instruments, 1/4 inch (6.35 mm) is standard (mostly mono), for headphones 3.5 mm (mostly stereo).