Google defines structured data as a standardised format for providing information about a page and classifying its content: that a page is a product, an FAQ, an article or an organisation, with its name, price, author and so on spelled out. The vocabulary most sites use comes from schema.org. Google supports three formats (JSON-LD, Microdata and RDFa) and recommends JSON-LD where your setup allows it.
JSON-LD is a small block of code in the page that visitors don’t see. It sits separately from the visible text, which makes it easy to add and maintain.
What it does and doesn’t do for AI answers: Google’s guidance on its AI search features says structured data isn’t required for generative AI search and that there is no special schema markup you need to add. It remains useful for rich results in ordinary search. The practical rule is that structured data must match what the page visibly says; it describes your content, it doesn’t replace it.
For brands, the visible page still matters most. See how to write a product page that AI answers can quote.