Not sure what the best definition would be. I think it doesn't involve the DLC levels for sure since not everyone has it without spending extra I think. All levels w/ DLC could be separate if that's the case. I'm not sure about bonus levels though. Otherwise it would just be the 50 main levels.

I did one run of all levels NG+ once (just the main 50), but it was bad and I had intended to do it again so it never got highlighted. It was somewhere around 1:20 for reference.