Authority: Leader, holder of power, someone with influence over opinions.
There are many kinds of authorities, but two distinctions are useful.
1. Authorities through power or influence: There are leaders who owe their leadership in the end to some kind of military, political or other kinds of power or violence, all of which are kinds of power, and there are leaders who owe their eminence to their abilities to influence the ideas of others, which is a kind of influence.
2. True and false authority: There are real and false authorities. Real authority is based on real power, force or knowledge, and is legitimate if claimed in these senses, however misled or evil the authority may be in effect, while false authority is based on a pretense of power, force, knowledge or insight, that is in the end based on the inability of those who are deceived to see through the deception.
By far the largest part of authority is based on authority about ideas or opinions, i.e. influence, and is mostly, when rationally investigated, a false authority: Even if, say, a medical doctor is honest and says all (and someone who is honest and does not hold back anything about a subject is rare), then still the patient lacks the medical and scientific knowledge to understand the judgements and recommendations of the doctor.
There are genuine authorities in fields of science and other knowledge, but the ordinary following of opinions of ordinary men is mostly based on the irrational following of leaders, often based on wishful thinking (to the effect that Our Leaders and Our Experts are obviously Benevolent and Good men and women with true or rational opinions, not because the sincere believers in this can prove this, but because this is what they have been told and like to believe).
An important reason for faithful following of false leaders in opinions, politics, religion and fashions of all kinds is the lack of general knowledge and education of their publics - many lies and poses of politicians and priests could have been seen through by their deceived publics if only the members of the public had given themselves more trouble to become informed about the subjects they are deceived about by those they believe to be authorities, or at least more informed about what makes an argument for something rational and non-fallacious.