The term client/server describes one possible relationship between two software applications in which the client makes a service request from the server. The client/server relationship can apply to two programs running on a single computer or two programs running over a network. In the case of a network, the client/server model provides a convenient way to interconnect programs that are distributed efficiently across different locations. Computer transactions using the client/server model are very common and it is likely you are involved with such transactions almost daily.
For example, to check your e-mail from your computer, a client program on your computer forwards your request to a server program at your Internet Service Provider (ISP). Once the server program has retrieved your e-mail, it forwards them to the client on your computer, which then allows you to read the e-mail.
The client/server model has become one of the central ideas of network computing. Most business applications being written today use the client/server model. A distinction used to be made between client/server applications and internet-based applications. However, that distinction is being blurred such that even internet-based applications are beginning to make use of the client/server model.
Using Visual Basic and SQL Server (or Oracle), I've built complex and highly-scalable client/server based systems for well-known international companies. Read more about the software I wrote and my role as a computer programmer for MasterCard International.