schema.org, originally called microdata, is a vocabulary for marking up structured data on the web. The schemas are designed to be machine-readable, so that they can be used by search engines and other applications. Using schemas allows webmasters to specify the data on their pages in a format that can be read easily by computers.
It comprises a set of microdata formats and guidelines describing how website content should be structured so that it can be understood and shown by these parties. It is developed by the Schema.org Consortium.
A schema is the specification of a structure, providing the actual definition of the objects it contains, and the relationships between them. The schemas of code and data have a one-to-one correspondence, and the same schema can refer to different codes. This means that a schema for data can have corresponding definitions of codes or types of codes.
In December 2013, Google announced that it would migrate its search results to exclusively use the Schema.org vocabulary for it’s index.
