Structured Data is Data that resides in fixed fields within a record or file. Relational databases and spreadsheets are examples of structured data. Although data in XML files are not fixed in location like traditional database records, they are nevertheless structured, because the data are tagged and can be accurately identified.
Structured data is becoming an increasingly important part of the web ecosystem. Google makes use of structured data in a number of ways including rich snippets which allow websites to highlight specific types of content in search results. Websites participate by marking up their content using industry-standard formats and schemas.
The schemas are different based upon industry and will be discussed in futher detail in posts to come.