This article is from the alt.usage.english FAQ, by Mark Israel firstname.lastname@example.org with numerous contributions by others.
Some people say things like: "It is not correct that it is the
biblical meaning. The biblical meaning of a man's knowing a woman
is such total love as to know all about her, which includes
intercourse. It is not an evasive term for one-night stands."
Not so. The Biblical sense of "to know" is simply "to fuck", as
you can see from Genesis 19:4-8 : "[...] the men of Sodom
compassed the house round [...] and they called unto Lot, and said
unto him, 'Where are the men which came in to thee this night?
Bring them out unto us, that we may KNOW them.' And Lot [...] said
[...] 'Behold now, I have two daughters which have not KNOWN man;
let me, I pray you, bring them out unto you [...]'"
The Hebrew word here is "yada" (yod daleth ayin). The Greek
word "gino:sko:" is used similarly in the New Testament.