This isn’t a stereo connector. And what I mean by that is a cable is what you send down it. Your headphones may use a cable that looks like this, but it’s not magically combining a stereo signal.
There are two cables in here. The left channel and a right channel. Each requires two connections.
This is called the tip and that’s the sleeve and this is called a TS cable. This particular cable has two TS connectors. We would expect these to carry two mono signals.
These two quarter inch TS cables terminate to this 3.5 millimeter TRS cable. The R is for ring. The sleeve is shared and it’s the return signal for these two connections.
We can confirm that with a tester. Notice this and this are not connected. None of these are connected, but this and this, this and this are connected.
That’s how we get two signals down what you are probably calling a stereo connector. But it’s only stereo if that’s what you’re sending down it. This is a quarter inch TRS.
If we open it up, you’ll see three wires inside and while this could be used for a stereo signal, in this case it’s wired into an XLR plug. Also a three conductor cable used for sending a balanced mono signal. Here’s an XLR cable used to send MIDI.
A cable is what you send down it and defined by how many wires are in it and by the anatomy of the connector. This one’s TRRS and it’s used for a phone. Left and right, the microphone and they all share a ground.
Call it whatever you want, but this isn’t what makes it stereo. You can share that with someone who belongs in a
