JSON is an Acronym for JavaScript Object Notation.

A serialization format for nested DataStructures that uses a tiny subset of JavaScript syntax: the shorthand notations for objects and arrays.

For some applications such as messaging, it has been gaining in favour of more complex notations such as XML and YAML because it has very low syntax overhead and is truly trivial to parse. As such, it is particularly well-suited for passing data among programs written in different languages (the common scenario being a server-side application written in Perl, Python or Ruby communicating with an AJAXified JavaScript client).