When a friend tells you she's not yet had sex with someone, what do you take that to mean? In all truth, studies show that the two of you might be thinking very different things.
In fact, about 37 percent of women consider oral sex "sex" — and 63 percent of them don't. Men are more likely to consider oral sex to be "sex." Different people consider different things "cheating" — just look at Mark Sanford, who said yesterday he'd not had sex with anyone else but had danced with other women when married men ought not do that.
To a degree, it's probably partly generational — I first realized that other people's definitions of what constitutes "sex" differed from mine in 1998 when I blurted out in class that Clinton hadn't "had sex" with Monica Lewinsky, it was just oral. Suffice it to say, I got some pretty interesting looks from some of my more conservative classmates... and my professor. In his mind, Clinton had, indeed, "had sex" with Monica Lewinsky; in my mind, "sex" was vaginal or anal penetration, and fellatio and cunnilingus didn't "count."
My gay friends schooled me on this point as well. While one professed to be saving his ass for marriage (literally), he didn't consider himself to not be having sex when going down on men; my lesbian pals wondered aloud what the hell kind of terrible oral sex I was having by comparison that I didn't consider it "sex." Yet, somehow, I continued, for a while, to consider oral pleasures less intimate than penetrative sex and, therefore, not "sex." And if surveys are correct, I was not alone — hell, if all the stories about people engaging in anal sex to avoid virginity loss is true, it appears that even the definitions of my teenage years have gotten a bit... stretched.
Looking back on it, though, it's all rather a lot of self-justification based on a desire to engage in sexual activity (and give and receive sexual pleasure) and the rampant, heteronormative concept that "actual" sex involves a penis penetrating a vagina. It seems, to me, to be tied up quite nicely in Jessica Valenti's concept of the "purity myth" in which virginity and so-called Godly sex is mythologized and fetishized to a point where there is no sex in our minds but that which could result in procreation — regardless of the similar health risks of oral sex and the intimacy involved in performing it... or engaging in anal penetration.