SEO & performance
Schema markup
Schema markup, or structured data, is machine-readable information added to a page that describes what it is: an article, a product, a business, a set of questions. It helps search engines understand content and can enable richer result displays.
The vocabulary comes from schema.org and the usual format is JSON-LD, a block in the page head that describes the page's entities and how they relate. A service page might declare a Service provided by an Organization; an article declares its author, date and image; an FAQ section declares each question and answer.
The benefit is precision. Search engines infer a great deal from page text, but structured data removes ambiguity: this is the business, this is its address, this is the article's publication date. Some types also qualify for enhanced results, though that is a possibility rather than a promise and depends on the search engine's judgement.
The rule is that markup must match what the page visibly says. Declaring reviews that are not on the page, or a business address the page does not show anywhere, is treated as spam. Structured data describes the page; it does not add claims to it.
Structured data as part of SEOSEO & performance