JSON
JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. It is based on a subset of the JavaScript Programming Language, Standard ECMA-262 3rd Edition - December 1999. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language.
JSON is pretty ubiquitous these days in web programming. An example is the JIRA bug tracker from Atlassian software which exposes it's data via API calls in JSON format. When working with large JSON data sets, it's helpful to have a viewer like http://jsonviewer.stack.hu/ which easily parses and renders the object in a tree fashion.