When using my iMac as a external monitor

[Shivetya]

for a Windows machine can I toggle back to the Mac desktop or is the system required to be off?

I was never sure of how that worked

 

[spinnerlys]

The computer is still running.

Applications running on the 27-inch iMac computer remain open and running while it is in Target Display mode.

from Using a 27-inch iMac as an external display

via search "imac target display mode" or "imac 27 as external display"

 

[Shivetya]

thank you, didn't recall the term "target mode"