Elasticsearch is a JSON document store

As you might have noticed from the response body of our API call, Elasticsearch stores data in JavaScript Object Notation (JSON) format. This allows developers to store objects with more complex (often nested) structures when compared to relational databases that impose a flat structure with rows and tables.

That's not to say document databases are better than relational databases, or vice versa; they are different and their suitability depends on their use.