Domain authority is a measure of the power of a domain name and is one of many search engine ranking factors. Domain authority is based on three factors: Age, Popularity, and Size.
SEO gurus Moz can be credited with the metric known as DA or domain authority. Moz’s own search algorithm gauges the quality of any given site based on a huge complex combination of factors including onsite and offsite, taking in to account things such as diversity of Backlinking domains to come up with a score between 0 and 100. A brand new site, for example, will have 0 whereas a very high authority site might have 80/100. Domain Authority gives those working in the field of online marketing a useful metric by which to consider the apparent quality of any site.