Authority is used to communicate a websites ability to rank well in the search results.
The word authority is normally used to describe a big player in an industry, an organisation or individual that has a lot of power. It’s the same similar principle but in the search engine world. If a website has a high authority number, the chances are it will rank high in the search results because Google has a lot of trust in that website and the content it regularly distributes.
Authority, from an SEO perspective, is broken down into two areas: domain authority (DA) and page authority (PA). There are lots of factors that come into play with obtaining a high DA and PA, such as: domain age, link equity, high-quality content, traffic trends, internal linking, strong on-page optimisation and more.
Be advised that the search engines are working hard to regularly tweak their algorithms and the processes involved in ensuring that the results are accurate, relevant and informational to the user. They do this by balancing their relevancy algorithms to determine what is suitable and what isn’t based on a sites topical trust flow and their overall authority. A site that’s considered authoritative in the eyes of Google is Wikipedia, as they have lots of links from other authoritative domains, good use of internal linking and lots of linkable content.