Definition: In the computer networking section, there are many computers that work together to transfer data and communicate with each other but it would not be achieved till an organized system manage the network, delegate tasks and monitor how the network works. There are many computers with specified jobs and different priorities. Some of them are Clients that are designed to use applications that are stored on other systems and access to remote services. On the other hand there are Servers, a server is a computer that provides services to other computer (and their users), in the same or other computer. The term client-server refers to a popular model for computer networking that utilizes client and server devices each designed for specific purposes.
Example: The client-server model can be used on the Internet as well as local area networks (LANs).
Examples of client-server systems on the Internet include Web browsers and Web servers, FTP (File Transfer Protocol) clients and servers, and DNS (Domain Name Service). About.com (2009)

History: Client-server architecture only became a reality with the advent of personal computers (PCs). Before PCs, programs were written for mainframes. Software written for mainframes was often coded in a monolithic format that is, the user interface, business logic, and data access functionality are all contained in a single application. Because the entire application ran within the mainframe this was not a problem.
With the advent of PCs, it became possible to offload some application processing onto a PC user's desktop. Because of this possibility and because it was economically expedient for many applications to use this paradigm, client-server architecture developed. Orbix.com (2006)

Current status: Nowadays, companies that want to develop their industries and businesses must have a well functional computer network running on their enterprise to automate tasks. It is not possible to achieve this goal without deploying a comprehensive and hierarchical network infrastructure like client-server architecture.

There are three types of client that connect to servers as the follow:

I. Thin
II. Thick

A thin client (sometimes also called a lean or slim client) is a client computer or client software in client-server architecture networks which depends primarily on the central server for processing activities, and mainly focuses on conveying input and output between the user and the remote server. In contrast, a thick or fat client does as much processing as possible and passes only data for communications and storage to the server.
Many thin client devices run only web browsers or remote desktop software, meaning that all significant processing occurs on the server. However, recent devices marketed as thin clients can run complete operating systems such as Debian Linux, qualifying them as diskless nodes or hybrid clients. Some thin clients are also called "access terminals."
As a consequence, the term "thin client", in terms of hardware, has come to encompass any device marketed as, or used as, a thin client in the original definition – even if its actual capabilities are much greater. The term is also sometimes used in an even broader sense which includes diskless nodes.[
The thin client is a PC with less of everything. In designing a computer system, there are decisions to be made about processing, storage, software and user interface. With the reality of reliable high-speed networking, it is possible to change the location of any of these with respect to the others. A gigabit/s network is faster than a PCI bus and many hard drives, so each function can be in a different location. Choices will be made depending on the total cost, cost of operation, reliability, performance and usability of the system. The thin client is closely connected to the user interface.
In a thin client/server system, the only software that is installed on the thin client is the user interface, certain