What constitutes cheating?

I believe that the general population is split on what actually constitutes cheating between a couple.  Some say that sleeping with somebody else is cheating while others believe that simply wanting to be with someone else can be considered cheating.  There is quite a gray area between sleeping with someone and fantasizing about being with them and I wonder how soon into that gray area would one have to go in order to cheat.  For instance, let's say a girl with a boyfriend decides to go out to a bar, have some drinks and have a good time.  This good time would consist of dancing very closely with at least one guy in the style us young people call 'grinding'.  Essentially you're dry-humping on the dance floor and the consistent 'grinding' usually leads to later hookups.  Would you consider this type of dancing cheating?


I used to think that cheating meant a significant other kissing somebody else but I have since revised my definition.  I think that some significant flirting and close dancing could be enough to constitute cheating.  If you are with somebody in a monogamous relationship than what business do you have going out and grinding with people in a non-joking manner (meaning that a serious attraction lead to such dancing)?  Shouldn't your eyes be only for the person you are in love with?  I thought about it and I know that I would be quite angry if I had a girlfriend and I found out that she was out flirting and grinding with guys even if she did not kiss any one else.  When in a relationship it's important to know what you consider cheating before the foundation of the relationship is laid.  Everyone has their own definition, but if your partner wants to be with someone else and acts on such desires with heavy flirting and some close dancing, isn't that just as bad as carrying out the act of kissing and/or sleeping with somebody else?