Domain Authority is a number invented by online SEO thought-leaders Moz, which is designed to approximate the website’s ‘strength’, ‘clout’, ‘respect’ or ‘propensity to rank well’.  Moz describe it like this:

“this metric is meant to approximate how competitive a given site is in Google.com”

Fancy, eh? Colloquially, you might hear people refer to domain authority (i.e: not the branded, proper noun) which broadly refers to a similar concept – how much inherent ‘good-will’ do the search engines seem to give to any page found on your domain name.

Does it matter? Why do we look at it?

We can’t know precisely the calculations done by Google, or Bing, or Baidu et al, when they calculate a page of search results.  However, we can have a good guess, and Moz are industry leaders when it comes to creating accurate models that we can use to predict their behaviour. 

In the absence of getting official numbers from Google’s shadowy inner machinery, Moz’ Domain Authority is a good way to get a quick indication of overall SEO health.  It’s also a score out of a hundred, which has quite broad appeal.

What influences it / what’s the solution?

If you want a real nitty gritty explanation of how this metric is calculated, you can read about domain authority on moz.com here.  The salient points:

• It is a logarithmic scale (easier to grow your score from 20 to 30 than it would be to grow from 70 to 80)
• It is based off many, many factors
• It uses a machine learning model to predictively find an algorithm that best correlates with rankings across thousands of search results that we predict against.

“Unlike other SEO metrics, Domain Authority is difficult to influence directly.

The best way to influence this metric is to improve your overall SEO. In particular, you should focus on your link profile—which influences MozRank and MozTrust—by getting more links from other well-linked-to pages.” - https://moz.com/learn/seo/domain-authority