The GData API is a Rest style web protocol to pragmatically interact with google applications and a services, like Google Docs, Contacts and Calendar etc.
The GData API is a rest style web protocol based on Atom/RSS. It can be used to query, modify and data hosted by Google's web based applications like Google Docs, Contacts and Calendar etc..
Google has wrapped the GData API to client libraries for Java, JavaScript, .NET, PHP, Python, Objective-C. If you are asking a question regarding the GData API and one of these client libraries ensure you include the tag for the language also.
For more information see: