Structured Data is how the data is suggested to be presented in a highly organized and predictable way for the search engines to more easily organize it and display it in creative ways.
Text based arrangement of data included in a file and served from the web is called Structured data markup which uses schema.org. JSON-LD (JSON-LD stands for JavaScript Object Notation for Linked Data) is the format used to very much easily represent structured data markup.
Google has developed a web tool to easily validate and test the structured data in websites. The link below drives you to the structured data verification tool.
https://search.google.com/structured-data/testing-tool/u/0/
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