Any markup that describes page content in a machine-readable format — most commonly JSON-LD using Schema.org types.
Structured data is the umbrella term. In 2026 it almost always means JSON-LD using Schema.org, but historically it has also covered microdata, RDFa, and site-specific feed formats (Open Graph, Twitter Cards, Product Feed).
The practical advice: pick one format (JSON-LD), ship it everywhere, validate it in CI. A partial structured-data footprint is worse than none because it confuses the retriever.
JavaScript Object Notation for Linked Data — the recommended wire format for Schema.org markup.
A shared vocabulary maintained by Google, Microsoft, Yahoo, and Yandex for describing entities on the web.
A JSON-LD block that describes the legal entity behind a site — name, logo, sameAs links, contact info.
A JSON-LD block that describes a page's place in the site hierarchy.