What is "system output?

So what is “system output?” There always seems to be something queued up in the tray at the bottom of the screen, and whatever seems to be queued up there is never anything I chose. (Or in most cases, not anything I would choose. For instance, right now Celine Dion is queued, and in my entire life I have never intentionally listened to Celine Dion. And it wasn’t anyone else either because no one else in my house even knows the Roon exists yet or, for that matter, listens to Celine Dion)

Anyhow, so this stuff is queued up and not playing. If I click play, I have no clue where it goes but no sound comes out of any zone in the Roon ecosystem. And whatever else was playing in other zones when I was last there remains in that zone’s queue.

So what is “system output?” Can’t find anything in basic audio setup or the KB about it.

System output is the basic OS audio device.

You probably have Roon Radio turned on. You’ll find a switch on the Queue screen that will let you turn it off.
When Roon Radio is on, it will select tracks it thinks you might like (despite the Celine Dion selection!) when your selected music is over. When Roon Radio is off, the music stops when your selected music is over.

In Windows (and possibly Mac OS) you can choose an active audio output for a computer. On my desktop computer I can choose between speakers, headphones or a toslink SPDIF connection to my DAC. The Roon Zone “System Output” sends audio to a computer and the operating system then sends it to the active audio output selected for that computer.