A special prosecutor (or special counsel or independent counsel) is a lawyer appointed to investigate and possibly prosecute a specific legal case of potential wrongdoing for which a conflict of interest exists for the usual prosecuting authority. For example, the investigation of an allegation against a sitting president or attorney general might be handled by a special prosecutor rather than an ordinary prosecutor, who would otherwise be in the position of investigating their own boss. Investigations into others connected to the government but not in a position of direct authority over the prosecutor, such as cabinet secretaries or election campaigns, have also been handled by special prosecutors.
The term is not specific to the United States, or to the federal government. According to Harriger, the concept originates in state law: "state courts have traditionally appointed special prosecutors when the regular government attorney was disqualified from a case, whether for incapacitation or interest." While the most prominent special prosecutors have been those appointed since the 1870s to investigate presidents and those connected to them, the term can also be used to refer to any prosecutor appointed to avoid a conflict of interest or appearance thereof. For example, because district attorneys' offices work closely with police, some activists argue that cases of police misconduct at the state and local level should be handled by "special prosecutors".
The term special counsel as used here is distinct from the United States Office of Special Counsel, which is a permanent government agency (unlike special counsels, who are appointed for specific, temporary assignments), which protects government whistleblowers, among other things.
The terms "special prosecutor", "independent counsel", and "special counsel" have the same fundamental meaning, and their use (at least at the federal level in the US) is generally differentiated by the time period to which they are being applied. The term "special prosecutor" was used throughout the Watergate era, but was replaced by the less confrontational "independent counsel" in the 1983 reauthorization of the Ethics in Government Act. Those appointed under that act after 1983 are generally referred to as independent counsels. Since the independent counsel law expired in 1999, the term special counsel has generally been used. This is the term used in the current US government regulations concerning the appointment of special counsels.
While the term special prosecutor is sometimes used in historical discussions of all such figures before 1983, the term special counsel appears to have been frequently used as well, including, for example, in contemporary newspaper accounts describing the first presidentially appointed special counsel in 1875.