Didn't miss anything - what are you talking about? A jack or a plug? I'm not aware of anything called a "jack plug" - mono or stereo. There are jacks and there are plugs.
type "jack plug" into google & your very first hit is a wikipedia for a TRS plug! If you've never heard a jack plug being referred to as an erhm a jack plug, well..... [heads off to look for an icon that shows shrugging shoulders, fails but settles for this
,to be fair the article suggests it's a Brit thing - news to me - so I consider the usage as going some way to settling the score for those overseas calling a water tap
Re Seven64's request .... if I'm reading it right, he wants a circuit to be 'switched on' when a headphone connector is pushed into the corresponding socket. Being a guitar rig, I assumed mono
...in which case it's quite easy to use a mono
headphone plug, to 'make' the ground connection between supply 0V & circuit 0v...the socket needs to be a TRS though (see how quickly I can adapt!) ....the supply ground connects to the TRS 'sleeve' lug ,the follow on circuit ground connects to the 'ring' lug .... a mono headphone plug gets plugged in ...the circuit 'supply' is made.....but you'd need to mod the headphone jack plug accordingly, which brings me onto this....
A mono plug simply won't do without modifying the headphone plug or using a stereo jack to mono plug adapter
Modding, changing, customizing, hey on occasion even using adapters ...it's the lifeblood of what we all do here!!