Why it matters to a buyer
Domain Authority is widely quoted in agency proposals and link-selling marketplaces as if it were an official Google score, and treating it that way leads buyers to judge a site or a link opportunity by the wrong number. It is genuinely useful as a rough, comparative signal, one site's DA against a competitor's, or one prospective link source against another, but it is Moz's own model, other tools publish their own similar but different scores, and none of them is what Google itself uses to rank a page.
How it is measured or applied
Moz calculates it from the quantity and quality of linking root domains pointing at a site, using a machine-learning model trained to correlate with search results, and it is recalculated regularly, so it moves as the wider web's link graph changes even if a site does nothing. It is checked in Moz's own tools or its free Link Explorer, and used mainly to compare like against like, tracking a site's own trend over time or ranking a shortlist of link prospects, rather than as a target number to chase for its own sake.
