An officer of the court was a member of the legal system who had an obligation to uphold the law and promote justice. Officers of the court included judges, lawyers and police officers.
Cardassian law maintained that a nestor must be an officer of the court. When Odo proposed serving in that capacity for Miles O'Brien in 2370, he was informed of this fact, to which he replied that he was one. Having been Terok Nor's security chief, he was granted this status six years earlier to allow him to testify in criminal cases. (DS9: "Tribunal")