Structured data is machine-readable metadata you add to a page (using the Schema.org vocabulary) that describes its content explicitly — "this is a Product priced $20" or "this is a Recipe with 30-min cook time." Search engines use it to understand the page and to show rich results.
JSON-LD — the recommended format
Google recommends JSON-LD: a <script> block in the head, separate from your visible markup.
