For convenience a domain name is normally assigned to each machine (for people remember names is easier than numbers)
The name is assigned meaning with the most general part on the right (opposite to IP addresses):
machine.subdomain.organization.country
or in our case, for ex.:
www.ictp.trieste.it
This allow the IP number to be changed while the user using the name sees no change
To convert names into numbers you need the Domain Name System (DNS), a hierarchical domain-based naming scheme with a distributed database system.