One of the main reasons why websites are not marked up is due to the confusion of what code to add and what each term means. Here are the differences of structured data, rich snippets, and schema to help clear that confusion.
Structure Data
Structure data is a term to describe when adding code on to a website, for instance, rich snippets, Schema and Twitter cards are all examples of structured data. Structured data is marked up so it can be understood more efficiently, especially by search engines. Google identifies and read structured data so that it can display rich snippets in its search results.
Rich Snippets
Rich Snippets are some extra information about a website’s content on search engine results page. Rich Snippets can show review stars, and aggregate rating reviews which can all be found the local box results.
Schema
Schema is an agreed term that websites use so it’s easier and consistent to create code to mark up their website pages so that they can be crawled better by search engines. For example, the company’s location, phone number, email address and products is what can be marked up so search engines can understand the meaning behind the content. Schema allows you to leverage the value of your content from your website so search engines can understand the purpose of the content, how to craw and index it but also how to characterize the most value to the content.