Schema markup and Schema.org
The shared vocabulary of types and properties that structured data uses to describe things on the web.
Schema.org is the shared vocabulary that structured data is written in. It defines types of things, such as Organization, Product, Event or FAQPage, and the properties each one can have, such as a product's price or an event's date. Google, Microsoft, Yahoo and Yandex started it in 2011, and it's maintained at schema.org.
Types and properties
Think of it as a set of forms. Each type is a form, and its properties are the fields. A Product has fields for its name, brand, price, availability and reviews. A LocalBusiness has fields for its address, opening hours and phone number.
For example, a dentist's website might describe the practice as a Dentist, which is a kind of LocalBusiness, with its address, its opening hours and the treatments it offers. A search engine reading that markup doesn't have to guess which of the numbers on the page is the phone number.
You write these types and properties into your page as code, most often as JSON-LD.
Which types matter most
Schema.org has hundreds of types, but most businesses only need a few. Organization or LocalBusiness for who you are, Product or Service for what you sell, Article for what you publish, and FAQPage for questions and answers. Google's structured data gallery shows which ones it uses in its results.
In AnswerOrbit
When a page fails the Structured data check in Page checks, we suggest the Schema.org types that fit what the page offers, such as Product, Service or FAQ. See Recommendations.