What Domain Authority is
Domain Authority, usually written as DA, is a score from 1 to 100 created by Moz that estimates how likely a domain is to rank in search results. Similar scores exist from other tools, like Ahrefs Domain Rating and Semrush Authority Score. They are built mostly on the size and quality of a site's backlink profile.
The key thing to understand up front is that none of these are Google metrics. Google does not publish a single authority number and has said repeatedly that no such score is used in ranking. These are useful third-party estimates, not the real algorithm.
How the score is calculated
Domain Authority is driven primarily by the number and quality of referring domains pointing at a site, modeled against what tends to rank. A new domain with no links starts near the bottom. A site with thousands of links from trusted publishers scores high.
Because the scale is logarithmic, moving from 20 to 30 is far easier than moving from 70 to 80. A jump in the high range represents an enormous amount of earned authority, which is why established brands cluster at the top and rarely get displaced.
How to use it without being misled
Domain Authority is most useful as a relative benchmark, not an absolute target. Comparing your score against direct competitors tells you roughly where you stand on link strength. Watching the trend over time tells you whether your link building is working.
It is misleading when treated as a goal in itself. Chasing a higher DA by buying low-quality links can raise the third-party score temporarily while doing nothing for, or even harming, real Google rankings. The score is a thermometer, not the thing you are trying to change.
What to track instead
Care about outcomes Google actually rewards: rankings for your money keywords, organic clicks and impressions in Search Console, and the quality and relevance of the sites linking to you. If those move in the right direction, the authority scores will follow on their own.