READ: Types of Applications
Client/Server applications
A program that is installed on multiple computers and runs over a network. Typically, these programs consist of a single server application and several client applications. For example, a server application has been installed on Computer 1 in the image below.
You install a client application on Computers 2, 3, 4, 5, 6, and 7. The program on Computers 2-7 have to access the application on Computer 1 in order to work. The popular game World of Warcraft is exactly this: Installing WOW on your computer does no good unless the game can access the WOW servers.
The primary benefit to client/server applications is that multiple people can be working with the same data at the same time. In the WOW example, multiple players are playing in the same game at the same time.
Another example of this is Instant Messenger. Have you ever noticed that your IM doesn't work if you aren't connected to the internet? That's because the client (on your computer) can't function without access to the server.