Third Precept: Abstention from Sexual Misconduct
This precept enjoins abstinence from improper or illicit sexual relations. The Atthasalini defines sexual misconduct as the volition arising in the body-door, through the unlawful intention of trespassing upon a person to whom one has no right of going.
There are four conditions for wrong conduct in sexual pleasures:
With reference to the first condition, there are twenty kinds of women with whom men should have no sexual relations. They can be divided into three groups, namely: women under the guardianship of parents, family members, relatives and authorities charged with their care; married or betrothed women; bhikkhunis and religious women observing the Holy Life. More here..