Structured data are markup tags in a page's code, invisible to humans, that describe its content in the schema.org standard – telling machines explicitly: this is a company, this is a product with a price, this is a question and its answer.
A search engine reading the text "from €2,500" can guess it's a price. Structured data removes the guesswork: "price": "2500", "priceCurrency": "EUR". The most popular format is JSON-LD – a data block in the page's code.
Benefits: rich results in Google (stars, FAQs, breadcrumbs – higher click-through) and intelligibility for AI: models and generative engines cite pages whose structure they understand unambiguously more readily.
Typical schemas for a company site: Organization, LocalBusiness, Service, FAQPage, Article, BreadcrumbList. You'll find all of them on this site – complete and validated.