>What is fat and thin client?
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It's a matter of the required resources on the local system to run the application - a thin client imposes minimal requirements for program execution on the client station, in most cases, the thin client does little if any processing other than handling the UI. A fat client carries the burden of program execution on the client machine - the more processing done at the client station, the 'fatter' the client must be to meet program needs.

As a vastly oversimplified example, things that run on a web browser, or on a remote terminal, where the local system displays screens and captures user responses to pass to the server at the other end of a wire are 'thin' clients; a VFP application where the program is loaded and executed on the client machine, and the client machine handles the UI as well as things like business logic and file I/O would be typical 'fat client' applications. The same VFP application run under Windows Terminal Server, where the bulk of execution is at the server rather than at the display console, would be run in a 'thin client' mode.