The connector's name is an initial derived from the names of three conducting parts of the plug: Tip, Ring, and Sleeve hence, TRS.
MX TRS connector also called an audio jack. MX TRS connector is cylindrical in shape, typically with three contacts, although sometimes with two (a TS connector) or four (a TRRS connector).
MX Mono jack is provided with a single normally closed (NC) contact, which is connected to the tip (live) connection when no plug is in the socket, and disconnected when a plug is inserted. Stereo sockets commonly provide two such NC contacts, one for the tip (left channel live) and one for the ring or collar (right channel live).