A website markup language created in cooperation by Google, Microsoft, Yahoo, and Yandex to help search engines better understand specific parts of a website.
It is a code that is added to the HTML of a website to give search engines more relevant information about a business, person, place, reviews, product, or thing. Proper schema markup can help your site display rich snippets in the search results page, making your search result stand out and improve clickthrough rates.
Learn more at Schema.org.