Domain Authority is a measure of the strength of a domain name and is one of many factors for search engine rankings. Authority domain is based on three factors: age, popularity, and size.
On the other hand, Page Authority or Authorities Page SEO is the term used to describe the probability that a particular page of your site will be found in search engines. Page Authority is based on a logarithmic scale from 0 to 100 and deals with the relevance of information and links in the web page of each other.
Internet Marketing