When you see an authority site you know it. They own the SERPS. Page 3 in Google will contain 3-10 listings from the domain. They will rank for anything which they have a targeted page for. In general they will rank between 1-3 for any phrase they target heavily. Backlinks are not an issue. Spammy backlinks cannot hurt them. They can violate anything. Penguin, Panda, EMD, too many ads, none of that will hurt them. Google updates which destroy others only bring them more traffic. Even the competitive terms, no work is needed as the weeks pass the site slowly and steadily climbs the SERPS.
That's is how you know an Authority Site.