Many people ask what this is and why is it important. It is actually pretty simple and straightforward. A Page is one page analysis while a domain encompasses everything housed inside of the domain including sub domains. So a website will include all the pages since they are all within the domain itself. A Home page will only measure that page for a Page Authority. (See definition below.)
Whereas Page Authority measures the predictive ranking strength of a single page, Domain Authority measures the strength of entire domains or subdomains. The metrics are, however, calculated using the same methodology — so in many ways, they’re more alike than they are different. (Reference- Moz.com)
