The client-server model for data exchange sets up a way to exchange data among applications. If you think of the Internet as a sort of plumbing for data transfer, a common model for sloshing the data back and forth is called the client-server model. A client-server model for networked computer systems involves three components: the client, the server, and the network. A client is a software application that most often runs on the end user's computer host. A server is a software application that most often runs on the information provider's computer host. Client software can be customized to the user's hardware system, and acts as an interface from that system to information provided on the server. If you are reading this text using a World Wide Web browser, you are using a client that understand the hypertext transfer protocol, the rules by which web sites share information with people using browsers to request it.
A server is sort of like a television broadcast station, making its information available to anyone who would like to receive it. Clients are like television sets--you tune it in to the station you want to watch. The television broadcast station sends the signal in a standard format which is ready for viewing by any kind of television set--black and white, color, big screen, whatever. You don't have to create different versions of Gilligan's Island for different television sets.