Schema or micro data is a system that was developed to create structured data markup supported by the major search engines (Google, Bing, Yandex and Yahoo!). This input provides search engines with additional or more accurate information about a web page and allows them to present the page to users in the most effective way. You can find definitions and documentation of for each type of schema on Schema.org, where you will find a collection of shared vocabularies webmasters can use to mark up their pages. While much if this data is not required by search engines, it is a great way to create separation from your competition and improve the user experience of your site. It makes information on your site easier to interpret for search engines, which can prove to have many useful functions. A common type many people see every day is used to define review rating of products, which are commonly seen in search results pages now. More importantly, new uses for schema are being developed on a regular basis and this is a great area to explore as you are developing or adjusting a website new website ideas.