Definition
E-E-A-T is Google's framing of the qualities its raters look for in content: first-hand experience, expertise, authoritativeness and trust. It is a quality guideline rather than a computed score, and it long predates answer engines.
Why it matters
The machine-readable parts of it transfer directly to GEO: a named author with a verifiable background, a dated page, cited primary sources, and a clearly identified organisation behind the site.
How to measure it
Audit whether each of those is actually present in the markup and on the page, rather than trying to estimate a score. Absent author and date fields are the two most common and most fixable gaps.