Extended definition
Umbrella term for any structured markup (schema.org, microdata, RDFa). In practice, JSON-LD via schema.org is the current standard.
Context and application
Three historical formats: 1) Microdata (HTML attributes itemscope, itemprop — old, still supported), 2) RDFa (from semantic web, rarely used in SEO), 3) JSON-LD (separate block in head/body — preferred by Google since 2015). In 2026, write JSON-LD by default. Vocabulary: schema.org (defined by Google + Yahoo + Bing + Yandex consortium). Rare types used in classic SEO: Event, Recipe, JobPosting, Course, SoftwareApplication, BreadcrumbList. Combine multiple types in the same @graph for complex pages.