Schema markup is structured data added to a web page in a machine-readable format (JSON-LD, Microdata, or RDFa) that tells search engines exactly what the content represents: a product, an article, a business, a person, a FAQ.
Schema powers rich results: star ratings in search, FAQ dropdowns, event dates, recipe cards. In the AI-search era, schema is also how Google’s answer engines identify what to cite. Every important page on a modern site should have some form of schema.