Abstaining from sexual misconduct is an important precept for both lay and ordained people. It is found in the Five Precepts, the Eight Precepts, the Noble Eightfold Path under "Right Action", as well as in the Parajika-dharma section of the Pratimoksha Vows of monks and nuns. Right Action (together with Right Speech and Right Livelihood) falls under the "Morality" section of the Three Higher Trainings. It is essential for the attainment of inner peace. Incidentally, the three types of wrong bodily conduct (i.e. killing, stealing and sexual misconduct) are the same in the Noble Eightfold Path as well as in the Ten Non-Virtuous Actions (or Refuge Vows).
Sexual misconduct is a non-virtuous action of the body which will cause pain and suffering to others. Examples are adultery (for this causes the breaking up of marriage), rape, intercourse with minors, etc, and the perversion of others. Buddhists believe that it is a cause for rebirth in the animal realm. Moreover, by avoiding sexual misconduct, one can protect the unity and well-being of families.
There are no grey areas because I find the Buddhist precepts for both lay and ordained people very clear and precise. But there are differences in degree of severity between the types of vows. For example, in the Eight Precepts, the third precept is modified to "abstaining from sexual conduct", which means no sexual activity during the period of this one-day vow.
The difference for laypeople and ordained people is that in the precepts for laypeople, "abstaining from sexual misconduct" or in the case of the Eight Precepts, "abstaining from sexual conduct", is the third vow. For lay practitioners, the first vow, in order of the degree of severity, is "abstaining from killing". But for ordained people, the first vow in the Parajika-dharma section of the Pratimoksha Vows is "abstaining from sexual conduct". Parajika means "the defeats" and those who commit a parajika are expelled from the order.
