TRS connector

audio jack, phone plug, jack plug, stereo plug, mini-jack, or mini-stereo = TRS CONNECTOR

Typically with three contacts (1.balanced mono or unbalanced stereo),
with two (a TS connector = unbalanced mono) or
four (a TRRS connector).

2-conductor connectors for earpieces on transistor radios:
*3.5 mm = miniature
*2.5 mm =subminiature

4-conductor version is becoming a standard output connector for compact camcorders, providing stereo sound plus a video signal.
This interface is seen on some laptop computers and on the second-generation iPod Shuffle.

Optical connector used for TOSLINK
mainly on Portable Equipment;
hi-fi separates and similar tend to use the standard square connector
that is the same size as a 3.5 mm jack.