Carnal knowledge may be used in many different ways. It is to know the body or flesh, where "know" means have some form of sex with, as it is used in the Bible on several occasions. The term is sometimes considered antiquated, but there are actual laws that still refer to this sexual act and these exist in many places in the world. Exactly how sexual intercourse deemed carnal knowledge is defined, and exactly who would constitute participants in breaking a law of this type could be variable.
In the 19th and 20th century many laws existed prohibiting what was called carnal knowledge. Archaic definitions of it might extend to consensual or nonconsensual sex with people under the age of 10, to a flat out euphemism for rape. In the present laws that may refer to this act of sexual intercourse, definition tends to be much more limited.
Though there can certainly be exceptions, carnal knowledge is consensual sex. It is often either between minors, or between people who have a four-year or more age difference where one person is a minor. Other regions use the term statutory rape instead, or statutory rape may be defined as a greater age difference between consensual sexual partners.
It is possible that carnal knowledge of a minor is a felony act, which might also be defined as a sex crime in some places. This is very serious, and it should be restated that the minor’s consent does not make the behavior legal. The consent of the minor is likely only noted to differentiate this sexual intercourse from nonconsensual sexual acts that would be deemed rape. The more aggressive and violent the act without consent is would be likely to lead to greater charges, but this doesn’t mean a successful prosecution of a carnal knowledge case is free from ramifications for the person charged, and these might include lifetime registry as a sexual offender, prison time, and/or needing to claim conviction of a felony on things like job applications.
Sometimes carnal knowledge laws on the books are ignored, just as are statutory rape laws where significant age difference between sexual partners does not exist. This can’t always be depended upon, and the rare case may find its way to court. Especially in places where teens are sexually active while still under the age of 18, and particularly if partners are of disparate ages or one is 18 or older, it might become very important to understand if local laws have the potential to create criminal charges or legal messes. Such information may be available from places like Planned Parenthood, and it also could be found in criminal codes for a region. As with all other considerations involved with sexual intercourse at a young age, knowing legal consequences, if any, of carnal knowledge/statutory rape/sexual intercourse is of value.