Unofficial hearing in the context of U.S. Congress is a hearing conducted either by single Congressmen of the United States or other state or local legislative bodies in order to hear the testimony of the people. It's unofficial because they are not conducted by Congressional Committees of the United States Congress or the state or local executive or legislative bodies. They have no power to issue subpoenas or enforce them. Attendance to such a hearing is entirely voluntary. Usually they are conducted by members of the minority party.