Flirting is an art form, a dance, a bit of play, taken far too seriously by some.
It is the curse of our Puritan routes that holding hands is only for lovers, that hugs are only for the intimate and that a touch on the shoulder is an innuendo. It's a game. A game for new friends, complete strangers, old lovers, everyone.
Flirting is a form of the verb flirt, which the OED tells us was first used in the "to flirt with" sense in 1777. Flirting is, "To play at courtship; to practice coquetry; to make love without serious intentions." Dickens brought the term into more common use by using it to hint at playing. Everything from witty word play to Roman hands and Russian fingers has been known to fall under the word's large umbrella. One can even flirt with Death himself, thanks to the English language.
In such a litigation-obsessed society, what is play to one is harassment to another. That hand on the shoulder is a violation. You have to pick your playmates carefully and feel the rules out as you go. The fun is in finding the meaning and the apprehension comes from wondering if you're both working under the same pretense. Was the kiss on the forehead a greeting or a come-on? Are those looks just out of appreciation for a fine figure or an undressing with the eyes? Was that compliment the product of too much drink or mere overconfidence? The joys of ambiguity are certainly not lacking in this theater of human interaction.
The game isn't just for single players, though it's all too often assumed the attached are uninterested. It reminds you of what could have been or what could be. Even the most innocent touches can ignite the flames of a dying passion. Courteous gestures bring back memories. Sweet words melt ice. Egos are bolstered.
At the end of the night, what you call it isn't what's important. The warm glow you may or may not feel inside is.
Thanks to the OED for some historical perspective. | 
