Structured data
Structured data is machine-readable markup, usually JSON-LD using schema.org vocabulary, that describes what a page is about. It can make a page eligible for certain search result features. It is not a ranking signal in itself and it cannot contradict what the page visibly says.
Structured data answers a question the HTML cannot: this page is a recipe, this number is a rating, this date is when the event starts. Search engines use it to build rich results — review stars, FAQ accordions, event listings, breadcrumb trails.
Three things worth being precise about:
Eligibility, not entitlement. Valid markup makes a rich result possible. It does not guarantee one, and Google withdraws support for result types periodically, at which point correct markup simply stops producing anything.
It must match the visible page. Marking up a rating that does not appear on the page, or FAQ content the user cannot see, is a policy violation and results in the markup being ignored or the site receiving a manual action.
It is not a ranking factor. Google’s documentation is direct about this. Structured data affects presentation, and presentation affects click-through, which is a real benefit — but the mechanism is not “markup makes you rank”.
JSON-LD in a single <script type="application/ld+json"> block is the format
Google recommends. Cross-reference nodes with @id values rather than repeating
the same organisation or author details on every page.