Structured data is a standardized way of annotating the content of a web page so that machines - chiefly search engines - can understand not just the words on the page but what those words mean. Rather than guessing that a number is a price or a date is an event start time, structured data explicitly labels each piece, turning free-form content into clearly typed information.
The primary vocabulary for structured data on the web is schema.org, a shared set of types and properties maintained collaboratively by major search engines. It can be expressed in several formats, but JSON-LD is the recommended one. When you mark up a page as an Article, Product, Recipe, LocalBusiness, or Event, you give search engines an unambiguous description of the entity it represents.
The most visible payoff is rich results: enhanced search listings that can include star ratings, prices and availability, FAQ dropdowns, breadcrumb trails, event dates, and more. These enhanced listings occupy more space and attract more attention, often improving click-through rates even when the ranking position is unchanged. Structured data also feeds knowledge panels and voice-assistant answers.
Beyond rich results, structured data helps search engines build a more accurate model of your site and its relationships to entities in the world, which supports long-term visibility. The key requirements are accuracy - the markup must match visible content - and validity, since malformed or misleading structured data can be ignored or, in cases of abuse, trigger manual penalties.