Any standardized format (JSON-LD, microdata, RDFa) that adds machine-readable meaning to web content. Schema.org is the most widely adopted vocabulary.
Structured data is the umbrella; Schema.org markup is the specific implementation. Google and most AI engines prefer JSON-LD because it lives in a single <script> block in <head> and does not interfere with rendering.
Without structured data, AI engines have to infer meaning from raw HTML — an unreliable process. With it, you tell them exactly what an entity is. Audit yours with Google's Rich Results Test, Schema.org Validator, or VibecodeAEO's built-in schema audit.
VibecodeAEO scans your site for all AEO factors weekly and tells you exactly what to fix.