什么是Domain authority？
A third-party score (0-100) estimating how likely a domain is to rank, based mainly on its backlink profile. Not a Google metric.
Domain authority is a 0 to 100 score, invented by SEO tool vendors (Moz's Domain Authority, Ahrefs' Domain Rating, and similar), that estimates how likely a domain is to rank based mostly on the strength of its backlink profile. Google has repeatedly said it uses no such single sitewide score; this is a third-party estimate, not a ranking input.
Used properly, it is a comparison shorthand. Scores are logarithmic (moving from 60 to 70 is far harder than 20 to 30) and only meaningful relative to competitors: if the sites ranking for your target keyword score 70+ and you score 25, that keyword is a long campaign, and a longer-tail target is smarter. Used improperly, it becomes a vanity KPI, chased with junk links that raise the score while doing nothing for traffic. Judge SEO by rankings, impressions, and organic traffic; let authority scores inform which fights to pick.
Different vendors' scores are computed differently and are not comparable with each other, so pick one tool and stay consistent.