Authority links -- what makes a link an authority link?
One of the best ways of doing SEO work is to try to get what are known as authority links. These links tend to convey a lot more link juice than other links, however they also tend to be much harder to get. But just what are authority links anyway? What qualifies a website as being an authority website on a particular subject? The answer, as with so many other things in SEO is, it depends…

How Most People See an Authority Site

Most people tend to consider authority sites to be one of two basic types of websites. The first kind is simply a well known and well respected source for general knowledge, usually associated with a well known traditional media source.
For example, a link on the New York Times is usually considered to be an authority link on the theory that the New York Times would take the time to fact check anything they include on their website or in their newspaper. This isn’t always the case by the way, as I’ve seen many major newspapers make mistakes and only sometimes have they corrected them; however as a rule of thumb, a site like NYTimes.com is considered to provide good authority links.

The Second Kind of Authority Site

The other category of authority links is a little more nebulous. It’s where a particular website grows a following in a particular niche and as a result of having grown that following, they are now considered an authority even though the site isn’t run by a company which has a reputation (such as the above mentioned New York Times).
A good example of this in our industry might be Johnchow.com. John has become extremely well known and respected in the world of blogging for a living, however when he started out a few years ago, no one had heard his name and he had exactly zero authority in the world of SEO and blogging. There are any number of such sites on the web and they are also regularly targeted for authority links.

An Important Distinction Regarding PR

Another way that some people try to figure out the value of an authority link is by looking at the site’s PR or Page Rank. This is a Google program which checks on various websites and tries to assign each of them a ranking as to how much authority they happen to have. While this can be helpful and a link from a high PR website can also get you good link juice, it’s not necessarily going to be an authority link.
For example, Facebook.com has a PR10 ranking (the highest ranking there is). However because they don’t have expertise on any particular issue, just because you happen to get a link on the front page of Facebook (I actually don’t think it’s possible, but that’s another discussion), doesn’t mean you’ve found an authority link. It just means you have a high PR link, which is often more valuable than an authority link.
I think for example that most of us would rather be linked to from the front page of Facebook than from say the front page of the Journal of Foreign Affairs, even though Foreign Affairs is well respected as providing authority links and not just high PR links.