What do you consider to be sex? (Not sex the noun, sex the verb.) At what point would you say, to yourself or others, that you had sex with [that person]?
My current definition of sex is that both (or all) people are naked and both (or all) people have an orgasm or equivalent-to-them-reaction. That is not what most people (in my completely unscientific assumption) think of when you say “sex.” I think most people think of some type of penetration and lots of people think of penis-in-vagina.
This is why, when I’m talking to people about sex, I often use other qualifying words besides “sex.” I’ll say intercourse to mean penis-in-vagina…because up until this point when I went and looked it up in the dictionary, I thought that was the definition. (Side note: did you think that was what intercourse meant also? Apparently the word I was looking for is coitus.) And I’ll say oral, or oral sex, to mean fellatio or cunnilingus. (My sexual vocabulary is sure getting a workout today.)
I’ve also heard the idea that sex is only the act of penetration, and everything leading up to it is foreplay. (I’m pretty sure that’s the most usual description in the media.)
That’s not how I think of it at all. To me, everything before you take your clothes off is foreplay, and everything after it up through the mutual orgasms is sex. And I don’t like the idea that everything up to “actual sex” is “foreplay” because I think it cheapens the things you do before you have an orgasm. It makes it seem like it’s less fun, like the only point of having sex is to have an orgasm. And while that’s a big part of having sex, that’s not the only reason I do it. It’s because the entire scenario is fun, not just the climax.
Of course, I have exceptions to my definition. But my point isn’t to list them all out here, my point is that definitions of sex can be complex and confusing. That when you talk to someone about “sex” it can be important to define what exactly you mean by that.