Structured data is a standardized format for providing information about a page and classifying that content on the page; for example, on a recipe page, what are the ingredients, the cooking time, the temperature, the calories, and so on.
Structured data that uses Schema.org as a reference vocabulary and can be embedded in web pages using three formats:
Imagine a book supported in three different formats: ebook, paperback, and hardcover. Each has different weights, sizes and so on. So does Schema.org.