The following are commentarial definitions of the five precepts. (Source: Bhikkhu Bodhi's Wheel booklet "Going for Refuge and Taking the Precepts"
First- The taking of life is the volition of killing expressed through the doors of either body or speech, occasioning action which results in the cutting off of the life faculty in a living being, when there is a living being present and ( the perpetrator) perceives it as a living being.
Second- Taking what is not given is the volition with the thievish intent arousing the activity of appropriating an article belonging to another legally and blamelessly in one who perceives it as belonging to another.
Third- Sexual misconduct is the volition with sexual intent, occurring through the bodily door, causing transgression with an illicit partner. (The nature of an illicit partner is only defined in detail from the male point of view and includes twenty types of woman. These can be summarized into four categories; 1- a woman who is under the protection of elders, i.e. parents or other responsible guardians, in other words, a minor, 2- a woman prohibited by convention, i.e. a close relative (incest), 3 - a woman already betrothed or wed to another, and 4- a woman under religious vows of celibacy or any union forbidden by the laws of the land.)
Fourth- False speech is the volition with intent to deceive, occurring through the door of either body or speech, arousing the bodily or verbal effort of deceiving another.
Fifth- The taking of intoxicants is the volition leading to the bodily effort of ingesting distilled or fermented intoxicants. (The Pali may also be so interpreted as to include all intoxicants of whatever sort.)
Source-Bhikkhu Bodhi, Webbed by Punnadhammo Bhikkhu