קדשה, a harlot; an unmarried woman engaging in adultery (with a married man)

אל תחלל את בתך להזנותה, “do not desecrate your daughter by making her into a harlot;” Rashi, basing himself on Torat Kohanim, understands our verse as handing over one’s daughter to be used sexually in any setting other than that of wedlock. Nachmanides, severely limits this verse by stating that the term used here means only not to allow one’s daughter to become sexually involved with parties who because of legal restrictions could never offer marriage to such a girl. This, according to most authorities would mean that if the relationship would lead to marriage the penalty would be death, either by a court of law or by heavenly decree, karet. [Tthe disagreement, of course, does not touch on the ethics or morality of the situation, but on the legal implications of our verse. Ed.] The only scholar who considers what Rashi says as legally making such a daughter into a harlot when she sleeps with a male while she is unattached, is Rabbi Eliezer, whose opinion is not accepted by halachah.

You asked – that I should explain to you if the Biblical verse states, “And to a woman in the flow (niddah) of her impurity, you should not draw near to uncover her nakedness.” (Vayikra 18:19) –refers to every woman who is a niddah, whether a man’s wife or an unmarried woman? And if it is so, how is it that [the Rishonim] did not mention this?…
Answer: The matter is clear that intercourse with a niddah is prohibited, not only with a man’s wife, but whether with his wife, another man’s wife, or an unmarried woman…
What bothered you regarding Rashba and Ra’avad, how they did not mention in their books [that this applies to all women, and only discuss the prohibition in the context of] a man’s wife who is a niddah. I can answer you that they spoke regarding the common case… but I have no need to give you forced answer. But the reason is that their writings were to teach the people how act according to halakha with their wives, when they were ritually impure and when they were ritually pure. And they had no need to discuss the case of an unmarried woman, for sex with an unmarried would is forbidden even when she is not in her niddah period. According to Rambam this is a Biblical prohibition that one would receive lashes for, if a woman made herself available in this way, that is to say, to have sex in a way of fornication, and this would be included in the category of a “prostitute” [that the Torah forbids], although she does not sit in a booth of prostitutes (bordello) and make herself available to all.
According to those who argue against Rambam and state that intercourse with an unmarried woman is not prohibited by a negative Biblical prohibition and one who does this is not liable for lashes, nevertheless, having intercourse with her does entail a Rabbinic prohibition. For even just being in seclusion with an unmarried woman [who is not a niddah] is forbidden based on the enactment of the court of King David. How much more so is intercourse with her [forbidden]. There is also those who say that intercourse with an unmarried woman is forbidden according to the Torah, although not based on a Biblical prohibition, and there are no lashes, but it is forbidden based on a positive commandment, [to wit:] “If a man takes a wife and has intercourse with her,” [it is as if] the Torah is saying: if he wants to have intercourse, he must have intercourse in the context of marriage.
There are those who permit intercourse with an unmarried woman, provided that she is designated for him alone, and they have said that she is the pilegesh (concubine) [mentioned in the Torah]. Even this (a pilegesh) Rambam has forbidden to a lay person and stated that she is only permitted to a king, as he writes in his book of Shoftim, and this is a well-worn discussion, and there is no need here to go at length. Nevertheless, there is no one who fully permits intercourse with an unmarried woman in a way of fornication…
Now, what you were astounded about – how is it that the Rabbis did not institute immersion for an unmarried woman,, so that the masses would not stumble as a result of her (i.e., so a man having sex with her would not transgress the prohibition of niddah)? There is nothing to be astounded about! For since an unmarried woman is forbidden [even if she is not a niddah], as we have written, then the opposite is the case! If she were to immerse, that would create a stumbling (lead people to sin), for then people would be lenient regarding the prohibition that applies to her, since she would only be forbidden according to Rabbinic law…

(1) 1) (Vayikra 19:29) ("Do not profane your daughter to make her a harlot, lest the land fall into harlotry and the land be filled with lewdness.") "Do not profane your daughter to make her a harlot": I might think that (this means that) he (a Kohen) should not give her to a Levite or to an Israelite (in marriage, this being regarded as "profanation" in that she thus becomes unfit to eat terumah); it is, therefore, written "to make her a harlot." Scripture is speaking only of the "profanation" of harlotry.

(2) 2) And what is that? One's giving his single daughter to his neighbor, not for the sake of marriage, and, similarly, her giving herself, to this end.

Before the Giving of the Torah a man would encounter a woman in the marketplace, and if he and she desired,, he would per her fee and have intercourse with her on the crossroads and then go on his way. And such a woman is called a kedeishah (prostitute). Once the Torah was given, a prostitute became forbidden [to have intercourse with], as it states, “There shall not be a prostitute from the daughters of Israel” (Deut. 23:18). Therefore, whoever has intercourse with a woman for the purposes of fornication, without marriage, receives lashes because he had intercourse with a prostitute.

A woman is not considered to be married except by way of betrothal in which the kosher betrothal was done appropriately. However, if he were to lie with her by way of harlotry, without the name of betrothal, it is nothing (towards her status as being a married woman). Even if he lies with her with the intent of marriage, mutually agreed between him and her, she is not considered as his wife and even if she dedicated herself only for him, rather the opposite is true and he must be forced (by Beis Din) to send her away from his home. Rem"a: For certainly she would be considered an embarrassment for immersion in a mikveh and he will lie with her in ritual impurity (niddah); however, if she dedicates herself exclusively for him as his wife and she immerses for him, there are those who would say that this is allowed and she would be a Pilegesh as described in the Torah and there are those who say that this is forbidden and they should both get whiplashes from the Torah as they have transgressed the precept "don't be a harlot." A Kuti who marries a Kutis and even a Mumar who marries a Mumerres in their (non-Torah) customs and they convert (or want to follow Halacha) afterwards, we are not at all concerned that they had an appropriate betrothal and he is permitted to send her out her without a Get, even though he remained together with her many years, this relationship is not considered anything but simple harlotry (Rivash 6 and Terumat HaDeshen, Part I 209), see Halachah 149:6.

The Gemara concludes: And the halakha is that with regard to a gentile or slave who engaged in intercourse with a Jewish woman, the lineage of the offspring is unflawed, whether she was an unmarried or a married woman.