What is structured data?
Structured data is machine-readable markup — on the modern web, almost always JSON-LD using schema.org vocabulary — embedded in a page to state unambiguously what the page is about: who published it, who wrote it, what it answers, and how its entities relate. It is the layer search and answer engines read when they need facts rather than prose.
For AEO, a handful of types do most of the work. Organization and Person establish who is behind the content (feeding E-E-A-T); FAQPage and HowTo hand engines pre-extracted question–answer pairs and step lists; Article with dateModified proves freshness; BreadcrumbList maps site structure; WebSite ties it all to one entity. Consistency matters as much as presence — the same organization must carry the same @id and url on every page, or engines see several entities where there is one.
JSON-LD won as the format because it lives in one script tag, decoupled from the visible HTML — but that decoupling is also its failure mode: markup that drifts from what the page actually shows, or that never parses at all. Validating structured data — all three encodings, JSON-LD, Microdata, and RDFa — is a standard part of the toolkit’s audit.