DNS stands for ” Domain Name System” and helps resolving names to IP numbers, as it is much easier for people to remember logical names rather then a 12-digit number.
In internet environment for each of us DNS is translating www.domain.com to the IP address of the web server.
Domain is basically registered extension name in Top Level Domain controlled by Internet Governance organizations (IANA, ICANN, IETF / RFC, originally ARPA) controlling DNS root servers.
Example of Top Level Domains: .com .org .ie etc
When you registering your .com domain you subscribing to one of the resellers which are authorized to register such names to global root dns servers. It is up to reseller and Top Level Domain operator to charge or not for such name. You might come across alternate DNS structure. This is basically network of DNS servers operating independently of Internet Governance structures. As most international Internet Service Providers agreed to use only accepted by ICANN DNS root servers alt.dns servers are not very popular within ordinary internet users cloud.
Internet is free to use any open DNS server each internet user want, ISP’s are including such revolvers as part of service but any IT person can easily change it to their own or open DNS addresses.
Because Internet becoming so crowded ICANN agreed to register few new TLD’s like .mobi .info.
Domain names are closely related IP as whole Internet is based on IP addresses. IP address is (to simplify) like postal address. As each computer on internet requires both ways communication even when opening simple website, it requires address so reply to a request can find the recipient. Each computer in Internet has and IP address. It might be not visible on each computer as it might be running behind sub network using so called Internet Gateway (usually router) to get out to internet. To find out what is your ip just go to http://www.whatismyip.com/. But IP assigned to you might be dynamic (in fact 90% of home users), meaning it is changing frequently. This is up to ISP to find recipient with dynamic IP. It is getting complicated here so I am going to explain in separate post.
Now because of the very same reason Internet Governance Bodies decided to upgrade Internet technology to IPv6 (allowing 340 trillion trillion unique addresses – 3.4×1038). As you can guess not only domain names are limited, but also IP addresses. Up till now Internet globally was based totally on IPv4 (allowing 4.3 billion unique addresses). Currently this is main focus of most of the ISP’s around the world. But this is what is happening now as in close future will be global standard.
More about DNS Revolvers, Master and Slaves, DNS propagation and role of each DNS record soon in separate post.