Inactive/reserved domain name

A domain name is inactive when its delegation details (authoritative name servers) are not transmitted and when it has not been published in the .lu zone. As such, the domain name may not be used for services such as hosting websites or for electronic mail. 

IP address

An IP address is a technical identifier, assigned to each piece of equipment connected to the Internet, and that these use to communicate with each other. There are currently two formats of IP addresses: IPv6 and its predecessor IPv4.