A phone connector, or headphone jack, is a common electrical connector used primarily for analog audio signals.
A phone connector, also known as phone jack, audio jack, headphone jack or jack plug, is a common family of electrical connector typically used for analog signals, primarily audio.
It is cylindrical in shape, typically with two, three, four and, recently, five contacts. Three-contact versions are known as TRS connectors, where T stands for "tip", R stands for "ring" and S stands for "sleeve". Similarly, two-, four- and five- contact versions are called TS, TRRS and TRRRS connectors respectively.
The phone connector was invented for use in telephone switchboards in the 19th century and is still widely used. In its original configuration, the outside diameter of the "sleeve" conductor is 1/4 inch (6.35 millimetres). The "mini" connector has a diameter of 3.5 mm (0.14 in) and the "sub-mini" connector has a diameter of 2.5 mm (0.098 in).
Source: https://en.wikipedia.org/wiki/Phone_connector_(audio)
