Definition from Nolo’s Plain-English Law Dictionary
A lawyer who is elected or chosen by local government officials to represent the state government in criminal cases brought in a designated county or judicial district. A DA's duties typically include reviewing police arrest reports, deciding whether to bring criminal charges against arrested people, and prosecuting criminal cases in court. The DA may also supervise other attorneys, called Deputy District Attorneys or Assistant District Attorneys. In some states, a District Attorney may be called a Prosecuting Attorney, County Attorney, or State's Attorney. In the federal system, the equivalent to the DA is a United States Attorney. The country has many U.S. Attorneys, each appointed by the president, who supervise regional offices staffed with prosecutors called Assistant United States Attorneys.