Moz created the term Domain Authority (DA) in 2004 when they launched it as part of their SEO toolset. Rand Fishkin and the Moz team developed it as a proprietary scoring system to help SEOs predict a website's ranking potential without needing direct access to Google's actual algorithms. The metric runs from 1 to 100, calculated using machine learning against Google's search results and factoring in linking root domains, total links, MozRank, MozTrust, and other signals. Domain Authority became the default terminology in SEO conversations because Moz was the first major platform to package link equity into a single, easy-to-understand number. Before DA, practitioners talked about PageRank (Google's metric, retired from public view in 2016) or vaguely referenced "link strength." Moz filled that gap with a consistent, accessible benchmark. Competitors have since launched their own versions. Ahrefs calls theirs Domain Rating (DR), Semrush uses Authority Score, and Majestic has Citation Flow and Trust Flow. All measure roughly the same thing—backlink profile strength—but the algorithms differ, so a site might score 45 DA and 60 DR. None of these metrics are used by Google directly; they're third-party proxies. At Ottawa SEO, we track DA across our 500+ domain portfolio mostly for client reporting and quick comparisons, but we don't obsess over the number itself. A site with DA 25 and topical relevance will often outrank a DA 50 generic site in a specific niche. DA is useful shorthand when discussing link targets or portfolio valuation, but we prioritize referring domains, topical trust, and actual traffic over the score. The term stuck because Moz marketed it well and integrated it into widely used tools like MozBar and Link Explorer. When SEOs say "domain authority" in lowercase, they often mean the concept generically; when capitalized, it refers specifically to Moz's metric. Either way, Moz owns the origin and the trademark.