I'm 99% sure that you already heard about APIs or REST APIs, it's what Twitter, flickr and a lot more companies use to share they're resources with a consumer.
A consumer can be anything from a website (for example, showing your Twitter updates on your blog or personal website) to a desktop / mobile application (iPhone, Android, Windows Mobilem, ...).
This is possible because all information sent to and from the API is encoded in either two common, inter-platform language, XML and JSON.
The difference between a regular API and a REST API is on the way they work. A REST API requires two entities to work, a client and a server.
