The Definition of Cheating?

I had a discussion with some girlfriends recently about cheating, and it led to this question: What is the definition of cheating?

Obviously, if a couple has a monogamous relationship, and one has physical sexual contact with someone other than their partner, that’s cheating. And sexual contact is not limited merely to intercourse, despite what some (a certain former president) may try to claim.

But what about non-contact? What about cybersex or phonesex? Although there’s no actual contact between the people, in my opinion--and I think in the opinion of most people--it’s still very much cheating. It’s a conversation with someone other than your partner in which the sole purpose is to become sexually aroused, and maybe even find some sexual release, even if you’re finding that by...taking matters into your own hands .

So, that brings us to emotional cheating--an emotional affair. I have to admit that I have a problem understanding this concept. A married woman may have a male friend that she feels especially close to--maybe because they share similar values, beliefs, views, backgrounds, experiences, etc. She may spend quite a bit of time with him, because she enjoys his company. She may value his opinion, and therefore seek advice from him. She may discuss (non-sexual) things with him that she doesn’t discuss with her partner--maybe because her partner has no interest in those things. She may even occasionally lean on him a little bit for emotional support. She may even be a little physically attracted to him. The list of 'she may' could go on and on. BUT, is it actually cheating, provided that there’s no sexual contact/sexual talk? I struggle with seeing how it could be. Of course, I’m not saying it couldn’t become cheating. And if one weren’t careful/aware of the situation and the possible dangers/totally committed to their partner, it could become cheating very easily.

So, what’s your opinion? What is the definition of cheating?