What does "Not responding" imply?

I hope this is not too much a bonehead question, but what does it really mean when Windows flags a program as "Not responding"? Has Windows performed an action that should interrupt the program's execution but the program has not given control back to Windows - like a tight loop? (I assume in a single threaded environment, Windows itself would be dead in that case.)

Or does it imply that the program is waiting on an event that cannot happen - e.g. two threads in a deadlock?

Or does it imply something I haven't thought of?

Thanks. That helped.

vgkfan83 said:

If a man pisses off his girlfriend/wife, and he tries to talk to her, she'll ignore him....... She's "Not Responding". .lol

OK. I'll tell the vendor of the software I'm beta testing that I piss off their program ... repeatedly, but just for several minutes at a time. That should really help them debug it.

I'll look into that. Maybe they will want the dump. They didn't seem interested in Process Monitor traces I took.