Basic Networking.

Most simply put, a network is an interconnection of computers so that they may share resources among them, such as printers, files, and disk drives.

In any network there are 'clients' and 'servers.'  A client is a computer which utilizes one or more resources being made available to it by a server computer located on the same network.  A server is a computer which provides a resource for other computers (i.e., the clients) to access.

You probably have heard the terms 'peer-to-peer' and 'client-server' in reference to common types of networks.   The differences between these types is important to understand.

In a peer-to-peer network, which is often functionally limited to a handful of computers, each computer often serves as both a 'client' and 'server.'  Let's say computer A has a color inkjet printer directly connected to it, and computer B has a black and white laser printer directly connected.  Computer A is configured to allow Computer B to print to the color printer, and at the same time Computer B is configured to allow Computer A to print to the laser printer.  Computer A is a client when its user sends a print job to Computer B's laser printer, while Computer B acts as a server in that scenario.  Conversely, Computer B becomes the client when its user sends a print job to Computer A, and Computer A then plays the role of server.  As you can readily see in this example, both Computer A and Computer B wear both the 'client' and 'server' hats.  This is typical of a peer-to-peer networking configuration.

On to Client-Server Networking ...

Network: An interconnection of computers for access to sharable resources.

Client:   A computer which utilizes a resource being made available to it by another computer on a network.

Server:   A computer which makes one or more resources available to client computers on a network.  A server may be a specially-designed high-end computer, or it may simply be a typical desktop machine.

Resource:   Any utility provided on a computer which is recognizable and useful to one or more other computers on a network.  Typically, printers, files, programs, hard disk space, and the like.

Peer-to-peer Network: A network wherein the computers play the role of both client and server from time to time.

In the diagram above, computer A is a client of computer B (to use B's printer) and a server to B at the same time (to allow B to use A's printer).  The same is true of computer A.  This is standard peer-to-peer networking.