Page Authority (PA) is a score that Moz gives to each page on a website, based on factors such as the number of links pointing to that page. The Domain Authority (DA) is a score that Moz gives to each domain, based on factors such as the age of the domain and the number of links pointing to it. Both PA and DA are important factors in search engine optimization (SEO), and Moz's tools can help users to improve their rankings.