In its wider sense the web is a conglomeration of several things. Information passed electronically throughout the web is subjected to 7 levels of conversion, or layers. One of these is IP (Internet Protocol) . This is the layer at which the world wide web comes together.
The Internet Protocol is the common denominator for a number of different higher level protocols which we commonly use, the most well known being http (hypertext transfer protocol), but other equally important protocols used every day are ftp (file transfer protocol) , pop3 and smtp the email protocols, and less often used ones such as newsgroup and some which are now hardly ever used such as archie (for searching archives).
Added to these is a host of specialist purpose built processes such as MUD's for net-based Dungeons and Dragons Games, ssh Secure Shell for operating computers remotely, and the list goes on.
These protocols all use the same worldwide address book, like a telephone directory. Every computer that is on-line is given a numeric address by the software that attaches them to the net. This is four numbers seperated by dots. The numbers range between 0 and 255, and the number is called an IP address, because this is the part of all messages on the web that the Internet Protocol layer manages. It is the equivalent of a postal address or a telephone number. But numbers are dry objects and so we attach names to numbers called domain names. The domain name server is a program used by every Internet Service Provider to keep the directory of names and numbers up to date and to translate domain names into IP addresses. With millions of people on-line constantly creating new domain names, these programs have their work cut out.
Originally there was only one domain name server, and he was a person. People sent him an email asking for a domain name and he would type it up in a file at the bottom of a list of 100 or so other people, and then send a copy of the file out to everyone on the list so they could directly see where everyone elses address was on the net. This is the way our teleophone directories are published. But this file quickly grew long and by the time there were a 1000 computers on the list the guy wrote a program to automate both the file maintenance and sending out the updated file. Soon the file got to be really big and so only changes to the file were sent out and everyone else had a program to merge the changes with the file they already had.
The web was born when the number of address changes became too great to be handled at one point. Instead each node point on the net had a program which allowed a new address to be added if it did not conflict with any existing addresses it already had. The new address was then sent to a number of other nodes which updated their files and sent it on to other groups of nodes, operating like a telephone tree. People being assigned the same numbers or names in different places at the same time were avoided by allocating a bunch of numbers and names to each region and node. This is why domain names have a 2 character country suffix in them, and why IP addresses for New Zealand typically have 203 as the first of the four numbers.
So the web is a global computer address system in which domain names and their corresponding IP numbers are constantly updated.
On top of theis layer is a small number of different protocols or message types that can be sent to these addresses. Each protocol has a server program to receive and decode each special type of message. When you send an http request it goes to a computer which is running a special program which handles http requests. The program is typically called httpd on the computer but we generally call it the webserver. Similarly for mail there is a mail server, one for handling incoming mail and another for handling outgoing mail, and also an ftp server. The programs that request information from the servers are called clients, so your webbrowser is an http client. Your eamil program is an enail client. When you configure your email program you enter two server names, the smtp name for send mail, and the pop3 name for downloading mail. Similarly, if you want to transfer a file to or from another computer you must use an ftp client and the other computer must have an ftp server program running all the time to listen for any requests.