GraphQL is a new concept from Magento 2.3 version in Magento eCommerce. Using Graphql we can get sales order data. There are many default core module uses GraphQl for getting data like, Product, CMS Page, and Block, Customer module uses Graphql for getting data of a specific entity.
Declarative DB Schema:
Magento 2.3 introduces a new approach – declarative database schema, allowing developers to define database structures and changes in XML files, instead of defining with install scripts. Magento 2.3 will convert the XML schema files into SQL statements and perform them.
Asynchronous web API:
An asynchronous web endpoint intercepts messages to a Web API and writes them to the message queue. Each time the system accepts such an API request, it generates a UUID identifier. Magento includes this UUID when it adds the message to the queue. Then, a consumer reads the messages from the queue and executes them one-by-one.
Magento supports the following types of asynchronous requests:
I hope this will help though this is not the best possible description but I tried