Structured Schema.org markup is a small piece code add to the html of your page in a format that is easy to understand for machines (Google, Microsoft, Apple ...). It is not displayed to human users and is only used to clarify and confirm the information in a your pages.
This code takes the form of named pairs that explicitly communicate the precise nature of each piece of information to search engines. For more information you can visit the schema.org site or the Schema.org Wikipedia page.