I don't necessarily define flirting differently in terms of actions, but to me it has the connotation of being between two people who don't know each other very well. I've only been in a few relationships, and they've all gone in the same manner - we're brought together by circumstance, school, activities, work, etc. We find we get along well, and become friends. We become better and better friends, until it morphs into a relationship. I recognize that I'm not at all typical or normal, but it's worked for me.