A phone connector, also known as phone jack, audio jack, headphone jack or jack plug, is a family of electrical connectors typically used for analog audio signals. The standard is that a plug (described as the male connector) will connect with a jack (described as female).
The phone connector was invented for use in telephone switchboards in the 19th century and is still widely used.
The phone connector is cylindrical in shape, with a grooved tip to retain it. In its original audio configuration, it typically has two, three, four or, occasionally, five contacts. Three-contact versions are known as TRS connectors, where T stands for “tip”, R stands for “ring” and S stands for “sleeve”. Ring contacts are typically the same diameter as the sleeve, the long shank. Similarly, two-, four- and five- contact versions are called TS, TRRS and TRRRS connectors respectively. The outside diameter of the “sleeve” conductor is 6.35 millimetres (1⁄4 inch). 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).
A common connector for plugging in a standard pair of music headphones such as the ones found on music players, computers and most other electronic devices with audio outputs.
It can support stereo and/or microphone, depending on the number of separate connector rings on the jack.
Some phones offer only a 2.5 mm jack, which is a smaller variety of the same principle.
Headphones supplied with mobile phones usually have a mic somewhere along the cable and a remote button that allows for managing calls without using the phone.
Some manufacturers opt for placing a 3.5mm audio jack on this remote control instead of directly on the phone itself. The reason for this is that 3.5mm jacks take up quite a lot of internal space; plus, in this way the user gets to keep the remote control/mic functionality while using third-party headphones.