The 3rd precept is:
I undertake the training rule to avoid sexual misconduct.
How is this precept explained?
Marriage is defined differently in different cultures, so are the commonly accepted rules in a given society considered as non-misconduct? If not, how should one determine the scope of misconduct according to the precept?
In MN 41 (and elsewhere), the Buddha describes sexual misconduct as follows:
He is given over to misconduct in sexual desires: he has intercourse with such (women) as are protected by the mother, father, (mother and father), brother, sister, relatives, as have a husband, as entail a penalty, and also with those that are garlanded in token of betrothal.
(Ñanamoli, Trans)
The commentary explains this passage as follows:
Māturakkhitātiādīsu yaṃ pitari naṭṭhe vā mate vā ghāsacchādanādīhi paṭijaggamānā, vayapattaṃ kulaghare dassāmīti mātā rakkhati, ayaṃ māturakkhitā nāma. Etenupāyena piturakkhitādayopi veditabbā. Sabhāgakulāni pana kucchigatesupi gabbhesu katikaṃ karonti – ‘‘sace mayhaṃ putto hoti, tuyhaṃ dhītā, aññattha gantuṃ na labhissati, mayhaṃ puttasseva hotū’’ti. Evaṃ gabbhepi pariggahitā sassāmikā nāma. ‘‘Yo itthannāmaṃ itthiṃ gacchati, tassa ettako daṇḍo’’ti evaṃ gāmaṃ vā gehaṃ vā vīthiṃ vā uddissa ṭhapitadaṇḍā, pana saparidaṇḍā nāma. Antamaso mālāguṇaparikkhittāpīti yā sabbantimena paricchedena, ‘‘esā me bhariyā bhavissatī’’ti saññāya tassā upari kenaci mālāguṇaṃ khipantena mālāguṇamattenāpi parikkhittā hoti.
Rough translation:
In the case where the father is gone, or the mother provides support such as food and clothing, the mother guards [her] thinking "I will give [her] to a good family when she comes of age." This is called "protected by the mother". By the same means "protected by the father", etc., should be understood.
When families come together and, even when the fetuses have just reached the womb, make an agreement - "If I have a son and you a daughter, let there be no getting to go to another; let her be for my son." Even in the case of a fetus that is protected thus, it is called "having a husband".
"Whoever goes to a woman of such and such a name, such a penalty is for him." Thus, a penalty is established by a village or a house, or a street; this is called "as entail a penalty."
"Even to the extent of those who are garlanded" - to the last extreme of all, with the perception that "This woman will be my wife", by tossing some garland over her head, there is "those that are garlanded".
Soooo, it doesn't seem all that culturally dependent. Some points of note are:
Basically, the point is that breaching an existing relationship, including parental guardianship, is a breach of the precept. It doesn't seem likely that this would be affected by cultural norms; as the Buddha notes, as long as there is a claim and it is breached, it is wrong sexuality.
It's worth noting, of course, that in (Theravada) Buddhism all intentional sexual activity is inherently immoral; this precept just attempts to lay down some general principles for those unable to commit to celibacy.
The meaning of third precept is that one's actions must never be motivated by desire of sensual pleasure.
The Pali text for third precept says:
Kāmesumicchācāra veramaṇī sikkhāpadaṃ samādiyāmi.
veramaṇī sikkhāpadaṃ samādiyāmi is a standard phrase that means "I undertake the training rule to abstain from ..."
The key therefore is Kāmesumicchācāra, or, parsed out, Kamesu-Micchacara.
Kam-e-su is usually translated as "sexual" and Miccha-cara as "misconduct". Such a translation, however, is severely misreading a simple literal phrase.
Miccha, the antonym of samma, generally means "wrong", "low quality", "sloppy" and literally "opposite", "contrary". Cara means "conduct", or literally "going about", "walking". So far so good.
Kama, the root of kamesu, is often translated "lust" or "sensual pleasure" but its more precise meaning is fondness (combining such elements as love, desire, and taking pleasure in) for an object of material senses -- in other words "sensual fondness" -- not sexual but sensual!
The key to understanding this phrase though is -e-su in Kam-e-su, which gives it the meaning of "out of".
Together, the phrase reads "Misbehaving out of sensual fondness" (or "Going astray out of ..."). This gives it a very different meaning than "sexual misconduct".
The idea is, when one's mind is obsessed by an object of sensual pleasure, one's ability to reason about results and side-effects of one's acts gets severely impaired. One is then prone to making bad decisions, creating suffering for oneself and others. Instead, one should never act out of mere "sensual fondness"! One should act out of right understanding, out of compassion etc.
In short, sexual misconduct means performing any sexual act that will be harmful to yourself and/or others. Just because the act is consensual does not necessarily mean it won't hurt someone, as example in the case of adultery, the two people performing the act may consent to it, but it hurts another person and family. If the spouse consents and/or participates(like swinger couples for example), then it is not considered misconduct.
The Buddha advised against sexual activity with those who are "under the protection" of their family(minors), a promised or engaged person, dhamma(monks/nuns) etc.
"He avoids unlawful sexual intercourse, abstains from it. He has no intercourse with girls who are still under the protection of father or mother, brother, sister, or relative; nor with married women, nor female convicts; nor lastly with betrothed girls."
These are all situations that can cause much wide ranging trouble beyond the couple engaged in the act.
This link may be helpful for learning more about the 3rd precept, as there is much more to this precept then sexual misconduct.
From Buddhism and Sex by M. O'C. Walshe:
"What precisely, then, does the Third Precept imply for the ordinary lay Buddhist? Firstly, in common with all the other precepts, it is a rule of training. It is not a "commandment" from God, the Buddha, or anyone else saying: "Thou shalt not..." There are no such commandments in Buddhism. It is an undertaking by you to yourself, to do your best to observe a certain type of restraint, because you understand that it is a good thing to do. This must be clearly understood. If you don't think it is a good thing to do, you should not undertake it. If you do think it is a good thing to do, but doubt your ability to keep it, you should do your best, and probably, you can get some help and instruction to make it easier. If you feel it is a good thing to attempt to tread the Buddhist path, you may undertake this and the other precepts, with sincerity, in this spirit.
Secondly, what is the scope and purpose of this precept? The word kama means in Pali "sensual desire," which is not exclusively sexual. It is here used in a plural form which comes close to what is meant by the Biblical expression "the lusts of the flesh." Greed for food and other sensual pleasure is also included. Most people who are strongly addicted to sexual indulgence are also much drawn to other sense-pleasures. Though we are here only concerned with the sexual aspect, this point should be noted. For those with any grasp at all of Buddhist principles, the basic reason for such an injunction should be immediately obvious. Our dukkha — our feeling, of frustration and dissatisfaction with life — is rooted in our desires and cravings. The more these can be brought under control, the less dukkha we shall experience. It is as simple as that. But of course, that which is simple is not necessarily easy."
Sīlabbata-parāmāso is a fetter. Sīlabbata-parāmāso means, morality based on conformity to a social or religious standard of behavior. Based on this I would not compare the precept to "the commonly accepted rules in the society".
Combing two other answers,
In short, sexual misconduct means performing any sexual act that will be harmful to yourself and/or others.
and
The meaning of third precept is that one's actions must never be motivated by desire of sensual pleasure.
These two go hand in hand. When an individual is motivated by desire or sensual pleasure it can often be at the expense of hurting themselves and others.
With all due consideration,
Kāmesu-micchācārā is not translated as sexual misconduct, but as the misconduct of actions motivated by sensual pleasure. And the Pali terms for wanting sensual pleasure abound in the Buddha Dhamma for wrongful phenomena that are to be abandoned and prevented from arising, such as the hindrance kamacchanda desire for sense pleasure, abhijjha yearning, lobha wishing, raga lust, tanha craving, all of them rather interchangeably translated as phenomena driven by the pursuit of sensual pleasure.
The entire Teaching of the Enlightened One revolves around the concept of annihilating sensual pleasure. Kamatanha, craving for sensual pleasure, is the root of all suffering. The cessation of suffering comes with the elimination of this very craving. On the Noble Eightfold Path, the step of right intention starts with nekkhamma-sankappo, thoughts free from sensual pleasure while right concentration begins with vivicceva kamehi, detached from sensual pleasure.
Any attempt at reducing the meaning of kāmesu-micchācārā to any form of particular sexual misconduct is just an excuse for hiding from the truth and distorting the true doctrine, fueled by attachment to precisely sense pleasure. And as a proper characterization of this tendency, it belongs to the category of mental fetters called sīlabbata-parāmāsa, namely, valuing or holding in high regard false systems of morality.
Respectfully
