JSON (JavaScript Object Notation) is a JavaScript based method to store and access information. JSON is easy to parse and minimizes the processing time for data transfer between server and mobile app. JSON focuses more on content and less on formatting.

The below graph represent the number of characters used by 3 formats for the listings of books on e-commerce site.

REST API Web services

REST stands for Representational state transfer which is a style of web architecture defines the behavior of data transfer between applications and servers. It is a group of functions using which data can be interfaced between your mobile app and server via HTTP protocol. Real-time example of REST API is Twitter REST API which you may query to get the latest tweets, you can give research online query or hash tag and it will return the leads to JSON format.