Schema markup is code (semantic vocabulary) that you put on your website to help the search engines return more informative results for users. If you've ever used rich snippets, you'll understand exactly what schema markup is all about. Here's an example of a local business that has markup on its event schedule page.
Schema markup, found at Schema.org, is a form of microdata. Once added to a webpage, schema markup creates an enhanced description (commonly known as a rich snippet), which appears in search results.
Schema.org (often called Schema) is a semantic vocabulary of tags (or microdata) that you can add to your HTML to improve the way search engines read and represent your page in SERPs.