The word
sex properly refers to the trait of being male or female.
Sex is now commonly used to mean
sexual intercourse (aka
sexual congress). Not that anyone really has a problem with this usage.
The controversial usage is that of the word
gender. It is a grammatical term. A noun's gender is masculine, feminine, or neuter. According to Fowler c. 1926, if you use gender in a serious manner to mean "male or female", then you are an utter fool, and you should be beaten. Or something like that.
But wait, let's go back to the dictionary of Samuel Johnson ("SaJo") from 1755. His #1 definition of
gender is "a kind; a sort". What's the #2? "A sex." And #3 is the grammatical sense.
The third edition of Fowler's (1996) mentions that some people are using
gender outside of its grammatical sense, but Burchfield doesn't take a stand.
A sociology textbook I have defines
gender as social meanings related to biological sex. But then again, the word
sociology is a barbaric Latin(French)/Greek hybrid. I mean, really, who are they to give usage advice?
The big question: is it okay to use
gender instead of
sex? My answer: only to avoid confusion (e.g. the first Austin Powers movie--"Yes, please"). In general, though, this use of
gender should be avoided, because it makes the writer seem like a euphemizer. And that's bad.
Oddly enough, in the OED, one of the obsolete definitions of the verb
gender is "[to] copulate".