In simple terms, when you type a domain name into your browser, it knows to take a web address that humans can read, like www.yahoo.com, and convert it to a computer readable number called an IP number. An IP number looks like this: 216.109.112.135. But what makes this happen?

There are computers on the internet called DNS (domain name system) root servers that can either tell you what IP number goes with what domain name or which DNS server knows this translation. These other DNS servers are run by companies called doman name registrars. Some examples of this type of company are GoDaddy, DreamHost, and even Yahoo!

So when you ask for yahoo.com, your browser knows to query the root DNS server, which sends you to the DNS server of the yahoo.com registrar, which sends you to its IP address, 216.109.112.135.

Only one registrar server is authoritative for each domain name. If registrar A is authoritative for your domain name, it tells your web browser where to go to show your web page whenever your domain name is typed in. If you want to move the domain name to another registrar for some reason (price, service, etc.), registrar B for example, you have tell registrar A to stop being the authoritative server for the domain name, and make registrar B become the authoritative server. When the transfer is made, registrar B tells the root servers that it is the new authoritative server.

Now when you type in your domain name into your web browser, your web browser queries the root server and the root server queries registrar B’s DNS server. This is what is meant by transfering a domain name.