E-E-A-T stands for Experience, Expertise, Authoritativeness, and Trustworthiness: the framework Google's guidelines use to judge content quality. It isn't a single score; it's a cluster of signals about whether the people and brand behind a page can be trusted on the topic.
It matters beyond classic SEO because AI engines lean on the same kinds of signals when deciding which sources to ground an answer in and cite. Content with visible authorship, real first-hand experience, corroboration from reputable places, and clear trust markers (accurate information, transparency, a credible site) is safer for a model to quote.
For brands, E-E-A-T overlaps heavily with entity authority: being a well-established, consistently described, widely-corroborated entity is exactly what makes both Google and AI engines comfortable presenting you as the answer. It's a slow, compounding lever. Built through genuine expertise and third-party validation, not on-page tricks.