Carnal knowledge is an archaic or legal euphemism for sexual intercourse.The word "carnal" derives from latin carnalis, meaning "fleshly", and the word "knowledge" in this phrase derives from the "Biblical sense" of the word, which means "sexual relations".

In criminology, the phrase has had different meanings at different times and in different jurisdictions. While commonly a mere euphemism for sexual intercourse (not necessarily unlawful), different jurisdictions may define carnal knowledge as a specific sex act such as contact between a penis and vagina, some laws elaborating this to include even "slight penile penetration of female genitalia". The definition sometimes includes a set of sex acts that include anal sex and/or oral sex, while some statutes specifically exclude such acts. The law may specify that the sex act must result in ejaculation, and/or orgasm. Carnal knowledge has also sometimes meant sexual intercourse outside of marriage, and sometimes refers to sex with someone under the age of consent. The phrase is often found in this sense in modern legal usage, as the term "rape" implies lack of consent, and consent is considered irrelevant to such cases.
Source(s):
http://en.wikipedia.org/wiki/Carnal_know...