A domain name is your address online and is formed by the rules and procedures of the Domain Name System (DNS) which is a sociable naming system for assigning addresses to web servers and web pages.  Behind every domain name is a IP address which most viewers would not be interested in seeing so the domain name system gives every server a memorable and easy to remember address.

online address

 

levels

Domain names are put in order from right to left, like your name.  The family surname or general identifier is to the right and very common  whereas the specific name or identifier is to the left.

These identifiers are called "domains".

The top level domains (TLD, or parent domain) are to the far right of a domain name.  The second level domains (children and grandchildren) are in the middle. The machine name, often "www", is to the far left.  Domain name levels are separated by periods (dots).