The client is a process (program) that sends a message to a 
server process (program), requesting that the server 
perform a task (service).Client programs usually manage the 
user-interface portion of the application, validate data 
entered by the user, dispatch requests to server programs, 
and sometimes execute business logic. The client-based
process is the front- end of the application that the user 
sees and interacts with. The client process contains 
solution-specific logic and provides the interface between 
the user and the rest of the application system. The client 
process also manages the local resources that the user 
interacts with such as the monitor, keyboard, workstation 
CPU and peripherals. One of the key elements of a client 
workstation is the graphical user interface (GUI).   
Normally a part of operating system i.e. the window manager 
detects user actions, manages the windows on the display 
and displays the data in the windows.