AJAX

Javascript runs on the client (i.e. in the web browser) yet is static text that is downloaded as part of a web page. Because Javascript is executable code, web pages with Javascript enhancements can behave more like traditional software applications than simple static information pages. One of the more powerful Javascript directives can pull information from a website or service to change part of the current page - without reloading the whole page. This feature is often called AJAX (Asynchronous Javascript and XML). Here's an example.