Back in my day, "headless" meant a computer without a monitor, for example a server or a PC that had been repurposed to server duty.

We also had the opposite: before Xrandr or Xinerama, there was an older X feature called "Zaphod Mode" that allowed you to drive a graphics card's multiple outputs (on cards that supported such) mapping each to a different X "screen", Zaphod Beeblebrox, of The Hitchhiker's Guide to the Galaxy, had two heads, you see.