Extended definition
Score 0-100 calculated by Moz that estimates a domain's authority. Not officially Google — it's an approximation based on backlinks.
Context and application
DA is a Moz proprietary metric; Ahrefs has DR (Domain Rating); SEMrush has AS (Authority Score). All have different formulas, but correlate roughly — a site with DA 50 typically has DR 40-60. Common mistakes: 1) DA treated as Google authority (it’s not — Google publishes no score); 2) Outreach decisions based exclusively on DA (a site with DA 30 but real traffic and thematic relevance = better backlink than a site with DA 70 but zero traffic); 3) Obsessive optimization for DA growth (DA grows organically as a result of good SEO, not the goal itself).
In practice
useful for quick comparisons, but don't make decisions based on DA alone.