Definition
The canonical answer.
Structured data is machine-readable markup, commonly JSON-LD, that describes visible page content using schema.org terms such as Organization, Service and Article. Appropriate markup supports eligibility for some search features. It is not required for Google AI features and does not guarantee rankings
Worked example
In practice.
A pricing page that states its figures in Product and Offer markup gives engines an extractable price instead of prose to interpret. The practical rule is server-rendered markup that mirrors the visible content exactly: schema that claims what the page does not show is
Where this work happens: Search
Is this your constraint?
The free 30-minute consult tells you, live, on your