Structured data is a code that is written specifically for search engines in a way that they can understand and has a certain structure and form. Search engines read the codes and use them to make search result pages richer. Briefly, structured data informs search engines about the meaning of your data by classifying it.
Structured data allows you to communicate with search engines. Google immediately reads the information you provide and decides to demonstrate it in rich search results. Therefore, structured data is a tool by which you can give detailed information to Google about your web page. Google then uses this information to get a rich search result. Structured data is important for SEO. Because, it helps Google understand what your website and pages are about.