What is DA & PA in SEO?

PA(page authority) & DA(Domain authority).

PA describes the probability that a specific page from your site will be found on the search engine. Higher PA means the greater chance of your page showing up on the search engines.

Page authority is a metric, developed by SEOMoz, to predict the ability for a specific page to rank in search engines. Page authority uses a 0 to 100 logarithmic scale. A high Page authority score means your page has the potential to rank well in search engine results.

DA is very important for a website because it will help new pages of content (including blog posts) get indexed more quickly and have a better chance of ranking prominently in the search results.

Domain Authority (DA) is a search engine ranking score developed by Moz that predicts how well a website will rank on search engine result pages (SERPs). A Domain Authority score ranges from one to 100, with higher scores corresponding to a greater ability to rank.  

DA is calculated by evaluating linking root domains, number of total links, MozRank, MozTrust, etc. — into a single DA score. This score can then be used when comparing websites or tracking the "ranking strength" of a website over time

How DA & PA Score can be measured?

You can measure DA & PA Score using MOZ's Open Site Explorer or MozBar (Firefox Plugin or Chrome Extention) i.e., MOZ's free SEO toolbar

Page Authority is essentially the same idea, except it applies to a single page rather than an entire domain. Scores range from 1 to 100; the higher the score, the more likely the page will rank well in search engines.

Because the scores are assigned based on an algorithm, they are essentially a prediction of how well the domain or page will do.

Domain Authority is a metric created by Moz.com as a more accurate indication of the value of the site. Like PageRank, it is a logarithmic calculation of the authority of the site. Rising from a low 30 to 35 will be easier on this scale than rising from a high 80 to 85. A DA of 100 is the top ideal, while an unranked site would have a DA of zero.

You can check your websites DA and PA using the MOZ tool

Just enter your website url and click 'Search', you will get complete details of DA and PA about it.

How to Increase it?

1. Write good content for your website.
2. If possible increase backlink to your site from Other sites (It can be done using various White hat techniques, by posting articles on similar niche blogs, by using other websites forums etc)
3. By Creating good inbound links (Like : A post is about DA & PA, you can provide a similar article link in that post to user)
4. It is dependent on Domain Age also
5. Quality of traffic on your website