A domain name is an Internet address. The character set that form this address is used to identify this particular network site. Therefore, the Internet domain name is an identifier of any activity in the field of Internet (eg www.udl.es )
The most important feature of a domain name is that's unique, and two people or organizations can not have both the same domain name. The computers on the Internet are identified by a long number which is called IP addresses. As it is difficult to remember, domains were created to replace the numbers with words, and so facilitate memorization.