Rich Client applications !

An application is usually described as a 'rich client application' to distinguish it from applications that depend on communications with a server. A rich client application generally has a more advanced user interface. For example, an application running on a local computer using its native graphical user interface components would be a rich client application. It is likely to be capable of doing most of the processing itself with perhaps infrequent communications with a remote server as required. In contrast, the same functionality may be provided by a series of web pages which have a more limited user interface (simply the available form components within HTML) and require a round-trip to the server each time a page of data is completed (usually by hitting a button marked 'Submit' or similar).

Compare using a local mail client (a rich client application) with the service provided by webmail systems for example (although the boundary is somewhat blurred these days with the use of AJAX on sites such as GMail -- this allows some processing to be done on the client). Any applications on your local machine that can be used without network access (to some extent) will be rich client applications.

The concept also extends to the entire user environment itself. 'Fat' clients are more commonly used these days and can operate without any network connectivity (think a usual Windows, Solaris or GNU/Linux desktop). In contrast, thin clients, such as the Sun Ray, do little computing themselves and receive direction from some remote server.

The word 'client' in the term simply refers to the fact that the application receives requests from a user, whereas interaction with a server indirectly generally takes place via a client application. It does not necessarily infer the presence of a server, and there usually isn't one with rich clients.