Schema.org
The open vocabulary of structured data types used across search and AI engines.
Schema.org is a collaborative open vocabulary maintained by Google, Microsoft, Yahoo, and Yandex for structured data on the web. It defines types (Article, Person, Product, Event, etc.) and their properties.
When you add JSON-LD to a page, you reference Schema.org types via the @context and @type fields. Schema.org is the vocabulary; JSON-LD is the syntax.