If you are in induction, it is anything that is not on the plan. The whole point of induction is to get you off all the bad stuff you've been eating (and a confession here is that I chose to "cheat" on induction by drinking caffienated drinks and diet coke). I didn't consider these to stall my progress, but they are technically cheats.

As far as being in the other stages goes, it is anything that sends you over your carb limit for the day or the meal, or throws you out of ketosis. Bingeing on anything with sugar/flour/potatoes/rice/pasta/ice cream/chocolate is a cheat. You can also binge on LC stuff (nuts, cheese, LC candy, pork skins, etc.), which I think is a cheat, albeit a more "legal" one, and probably less damaging. I consider that to be different from having a bite or two (sometimes that is a sanity saver) of something that is high carb and then stopping. That's a taste (of course if your whole meal is tasting other people's HC stuff, that's a cheat too!). Anything that starts out with the thought - just this once/one, it can't hurt.....is probably a cheat.

I'm not sure where to put "cheats" that happen because you are eating at someone's house and all they put in front of you is high carb food. It is still a cheat, but an unavoidable one. Sometimes these things happen, and you just have to make the best of it and go back to induction for a few days to compensate. I think that to truly cheat, you have to choose to or allow yourself to be out of control.

this is all in my humble opinion...

Can you tell I went to law school?