what are harm principles?

In his essay on liberty john stuart mill propounded political theory callef harm principal. He says that their needs to be a difference between self regarding actions and other regarding actions . He argues that in the context of self regarding actions the state has no business to intefere.Inbthr contrast with respect to actions which have consequences on others actions may be taken and tge state may intefere.If such actions was harm to others thrn to protect a person from being harm its the duty of thr state to constrain a person from causing such harm . Mills recommends social disapproval for constraining a person . He believes that suchca constrain shoulf be suficient and the police must not be involved . Constraining actions by the force of law should only happen when the other regarding actions cause serious harm to definite individuals.