Expert

It is not at all easy to say what an expert is. This is actually studied in epistemology under the general heading [expert knowledge]?. On one account, put very roughly, an expert is a person who is (or, perhaps, is widely recognized to be) a reliable (see reliabilism) source of [knowledge by testimony]? for other people.

Can be contrasted with cranks, who think they know what they are talking about, but don't. And with academic elitism, a syndrome of those who think that ONLY they know what they are talking about, and no one else does