Domain Authority is a score based on a scale of 100 and an amalgam of many SEO factors that make Websites rank better than other Websites on Search Engine Result Pages (SERPs).
The key elements which make up the DA are - The Website’s Age, Popularity, Backlinks, MozRank, MozTrust, etc. Domain Authority was developed as a competitive metric to keep track of how well a Website is performing in comparison to its competitors.
The more the DA on a scale of 100, the better a Website is placed when it comes to Ranking on Search Engine Result Pages (SERPs).
How Can We Increase / Improve DA - There is no particular guide to improve a Website's DA, but there are ways in which you can definitely improve your Website’s Domain Authority.
Once done with creating quality content, next is to get them linked by some High Domain Authority Websites. Backlinks from a diverse range of High Domain Authority Websites can help increase a Website's DA considerably.