Launched in 2011, Schema.Org is a collaboration between Google, Bing and Yahoo to provide a standard structured base for presenting data to search engines. Their aim was to agree on certain standard layouts for information that is common to most websites. The initial collaborators were joined by the Russian search giant Yandex towards the end of 2011.
The layouts specified are extremely detailed and include:
Schema.org specified these structures (often in great detail), using three vocabularies:
When used as Microdata, the text enclosed in the structure will appear on the webpage as part of the visible content. JSON-LD is added as a script usually in the page header and is only visible to search engines.
Here is a simple Microdata markup snippet produced initially using the Schema Creator Tool and then modified slightly by hand. It represents an Organization – specifically a local business and is just one example of many possible schemas. When googlebot reads it, it will know that it designates a local business and thus will make it much easier for Google to use and format in results of search queries.
Based on the Microdata on a page, Google and other search engines will be able to highlight certain information that will be useful for the searcher.
By adding the structured data as rich snippets into search results, Google gives browsers more information about things like products, people, recipes, events and reviews. This allows website owners to better showcase their content and to provide users as much information as possible.
About Schema.org: https://en.wikipedia.org/wiki/Schema.org
Schema Creator tool:
A great resource for creating various schemas on-page. It currently produces only Microdata. http://schema-creator.org/
Google Structured Data Testing Tool: https://search.google.com/structured-data/testing-tool