What do you consider "cheating"?

I thought that we could personally just ask ourselves a few questions: Do I talk about my marital [or other relationship] problems with this person?
Do I create opportunities to be with him or her?
Do I hide the relationship from my spouse?
If my spouse were present, would I be embarrassed?
Would my spouse feel suspicious or betrayed if he or she overheard our conversations?.....I believe that boundaries are a personal thing...

Let say that sex, virtual sex or kiss maybe should be treated as cheating.