Structured data is a method that makes it easier for Google to understand the data in the content by adding it to HTML etc. Currently, it means to notify using Schema.org.
There are multiple setting methods, but the method using microdata is mainly used, and recently, the method using json + ld has also appeared.
Google is focusing on improving the convenience of Serps using structured data, and also provides testing tools and support tools.
Structured data markup support tool