Now let us understand the various terminologies used in SEO of a Website/page.

Starting with the first:

1. Domain Authority (DA): 

It is the information about a domain, which tells us how the search engine is working for our website. 

This is the authority given to a domain which has a value between 0-100. The more the Value, the much better the authority of a domain and thus good rank in Search Engine Results Page (SERP) for a particular query/keyword searched. The domain authority of a Domain depends on many factors:

a. Domain Age

b. No. of Internal Links. (Links from one page of a website to another page within the same website.)

c. No. of good quality backlinks pointing toward this domain.

You can easily check the DA of a website at BulkDAchecker

2. Page Authority (PA): 

Likewise, Domain authority, the page authority is the authority given by Search engines for a particular webpage of the website. It also depends on the Good quality backlinks pointing towards this page.

Note: Domain authority of a website is same, but page authority could be different for each page in a website.

You can check PA of a particular webpage at MOZ