Structured data is machine-readable markup (JSON-LD using Schema.org vocabulary) embedded in web pages that states facts explicitly — what a product is, what it costs, how it's rated — so crawlers and AI systems don't have to infer them.
For AI visibility, structured data serves the retrieval layer: pages with explicit Product, Organization, FAQ, and Review markup are easier to parse, quote, and cite correctly. It reduces the chance a model mangles your facts.
It is not a ranking hack — models do not reward markup for its own sake — but it removes ambiguity, and ambiguity is where misattribution and hallucination breed.