Parole is the conditional release of prisoners before they complete their sentence. Paroled prisoners are supervised by a public official, usually called a parole officer. If paroled prisoners violate the conditions of their release, they may be returned to prison. For example, paroled prisoners often must get and keep a job, avoid drugs and alcohol, avoid their victims, not commit any crimes, and report regularly to their parole officer. If a paroled prisoner violated his parole by violently assaulting someone, he would probably be returned to prison. If he ran a stop sign, he probably would not be.
Prisoners do not have a right to parole. Typically, prisoners are reviewed by a parole board, which determines whether to parole them and what conditions to place on their release. Rules regarding parole vary by jurisdiction. See, e.g., the United States Parole Commission website.