Sheriff, in the United States, a public official, usually elected, who is in charge of law enforcement in a county (or parish). A sheriffs principal duties are to enforce the law and to carry out decisions of the county court. A sheriff serves legal papers, summons jurors for the county court, and maintains the county jail. One or more deputy sheriffs may be appointed, and other persons may be deputized when needed. The office originated in England in about the ninth century. A sheriff was the king's overseer in a shire, the old term for county.
Prisons spy on inmates' telephone conversations to make sure the crooks aren't trafficking drugs or organizing gang riots from behind bars. But does this monitoring infringe on their rights?
If you need an analogy for PRISM, one apt comparison would be to HBO's show "The Wire." Just swap "U.S. government" for Baltimore police, "Internet data" for phone wiretaps, and name the target as "really anyone" instead of drug traffickers. Got it?