The HTTP API currently supports JSON and XML response formats.
JSON stands for JavaScript Object Notation and it is a lightweight data-interchange format. Since the JSON format is text only, it can easily be sent to and from a server, and used as a data format by any programming language. It is easy to convert a string, written in JSON format, into native JavaScript objects. If you receive data from a server, in JSON format, you can use it like any other object.
XML stands for eXtensible Markup Language and it is a markup language much like HTML. It was designed to store and transport data. XML data is known as self-describing or self-defining, meaning that the structure of the data is embedded with the data, thus when the data arrives there is no need to pre-build the structure to store the data. It is dynamically understood within the XML.