An authority site is a slightly generic and admittedly ambiguous term for a website with a great deal of authority. Perhaps the better question to answer is what gives a website authority, so let's address and answer the question of what is an authority site right now in this article.
What Is An Authority Site?
A site is said to have authority based on a small handful of criteria:
Links - The number of inbound links that website has from other reputable and relevant websites is of note. Keep in mind that quality supremely trumps quantity in regards to links every time. A site can have hundreds if not thousands of spammy "built" links from various websites around the internet, but it's the same site which has dozens or even just a handful of relevant EARNED links from other authority sites within its niche which is going to outrank that other site every single time.
Age - The age of a domain is very important, as well. This is why domaining is a big business with webmasters always looking for discarded or for sale websites from long ago which have a lot of built up authority just based on the fact that they've existed for 10 years or more. All things being equal, an older domain is going to outrank a newer domain every time.
Content - Content is still king, and having a lot of content on the focus of a website is a great way to get a reputation as an authority site. The more information which a website has on a particular subject, the more it will be seen as an authority on the subject which will move more webmasters to link to that site.
Traffic - This goes hand in hand with content and is frustrating for many marketers and webmasters to understand because it's a bit of a chicken and egg situation. The more traffic you have, the more your website will be regarded as an authority site in both the eyes of the search engines as well as the people who visit that site.
The concept of the authority site is like that of a snowball which continues to gain traction and grow. Domain age can't really be faked or helped in any way other than through time, but every new insightful post which is made in your niche increases your site's perceived authority and will continue to net you more and more traffic, not to mention links when other webmasters remember that you're the authority on your particular niche.
This really is the key to come away with here, however. Make sure that your website, your business, your product, your service, make sure that it excels in one specific area of interest and people will come looking for you every time.