The study concludes that there is a disagreement about what constitutes "having sex." We hate confusion, so we are going to break it down for you: "Having sex" means any consensual behavior between two or more individuals involving genital contact and bodily penetration. That means oral sex, anal sex, and vaginal sex are all "sex." Sorry, guys on the DL, even if you have anal sex (top or bottom) with guys means you still "have sex" with men. It is also "sex" if no orgasm or ejaculation occurs. If you put a penis (or vagina) in your mouth in a coat room for 30 seconds, you had "sex" with that person. It was probably short and unfulfilled for both parties, yes, but it was still sex. "Sex" also includes any activity that happens in the presence of prophylactics. Just because you wore a condom, does not mean you didn't bang that fat chick who lived in the room next to yours sophomore year.
This leaves some leeway for hand jobs, heavy petting, and general rubbing. However, if any of these behaviors occurred and the subject of sex is brought up, they must be acknowledged. It's like being charged with a felony but not convicted. So if you jerked a guy off in a New Jersey truck stop and someone asks, "Did you have sex today?" You can say, "No," but you must add, "But I did jerk someone off." Also, if you reached into a girl's pants and played around a bit while making out before being interrupted by your screaming wife who yells, "Are you having sex with her?" you can say, "No!" but you must add, "I was just playing around in her pants a bit."
That, everyone, is the definition of sex. It's kind of like pornography, it's hard to define, but we know it when we see it. The rest of it is just semantics so we can make ourselves not feel like dirty sluts or get away with cheating on a significant other. Really only lawyers and eight-year-olds play semantics and only religious prudes are ashamed of sex. And no one likes any of those.