Like a telephone number, a Domain name is a unique Identifier that points to a certain site on the World Wide Web. Each computer on the Internet has a unique numeric Internet Protocol address such as 18.104.22.168 . These numbers are not user-friendly and give no indication as to what this address contains.
A domain name is a mnemonic that is not only a lot easier to remember but that could also indicate what the Web Site contains. It is easier to remember old-books.www.pf677.com than 22.214.171.124 and, if you are a collector of old books, you have a fair idea that this site will contain information that you would find interesting.
Typically, Domain Names operate like telephone dialing codes in reverse. The first portion of the name points to a specific site, the second points to the broad category the site falls in and the third portion is the country code where the site is registered. For example, absa.www.pf677.com refers to Absa Bank's Web site. This site is registered in the commercial (co) domain in South Africa (za).
In all countries there are Domain Name Servers, computers that will take the Domain Name and look up the relevant Internet Protocol Address and feed this address back to your computer so that it can connect with the site you wish to visit.