Computer network (network) is a system that connects a minimum of 2 computers in order to share resources and access information. In an ideal computer network every node of the network can request as well as provide a service.
A computer requesting some service is called the client and the computer sending the requested resource is called the server. This design is called a client-server computing system. Before the concept of computer networks became a reality, the computers used to be standalone computing machines.
However, with the advent of inexpensive local area networks (LAN) in offices, client-server applications became common. In traditional client-server applications a powerful database server runs on the network and desktop applications run on local computers, accessing data over the network. In simple terms, Servers provide resources and Clients receive resources.
Web applications follow a similar client-server architecture. In the client-server architecture for internet applications the server is a computer which stores the required resources, namely data and code, to compose and serve the webpages. The webpages are served in response to the commands given to the server over the internet. The computer from which these commands are given is called client.
Let us see this in a little more detail, when you type the web address of a site (eg. yahoo.com) in the address bar of Firefox/Chrome browser (or any other web browser), the web browser sends a request to the server computer (host) over the internet to send the first page (called homepage) of the site. The server responds by sending the requested page to the web browser and then the web browser renders the webpage in the browser window.
In the initial Web development times, the browser requested an entire page, and it was generated with relevant data, and sent for rendering in the browser.
A modern approach involves a server providing access to resources in the form of XML or JSON messages, in response to client requests.
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