Domain authority is a measure of the power of a domain name and is one of many search engine ranking factors. Domain authority is based on three factors: Age, Popularity, and Size.
The search engines want to provide users with website results that can be trusted. New websites are popping up every day and many don’t last for various reasons. Domain age is an indicator of trust because it proves to the search engines that the website has longevity. If the website owner has maintained registration of a website consistently and has generated an increase in traffic to that domain over time, the search engines conclude that it must serve a purpose and be a trusted source.
Domain popularity is measured in part by the number of inbound links from quality sites that a domain has. Inbound links to a domain are a signal that that website has useful information that is worth sharing. This is why a white hat SEO link building campaign is so important. Tactics such as blogging and blog commenting, press release distribution, directory and profile submission, article marketing, and social media help to build inbound links to a domain and generate traffic over time.
The size of a website on a domain contributes towards its authority because the number of pages that exists on a domain correlate with the amount of content that can generate inbound links. A larger website with quality content on each page will have more inbound links than a smaller website.
Domain authority, or domain trust, is important because it will help new pages of content (including blog posts) get indexed more quickly and have a better chance of ranking prominently in the search results.