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A hostname is the unique human readable name by which a device attached to a network (which could consist of a computer, file server, network storage device, fax machine, copier, cable modem, etc.) is known on the network. Each hostname corresponds to an IP address. Hostnames were introduced because they are easier to remember than numerical addresses. On the Internet, a hostname is also called a domain name. Consider the example "ecolotrain.uni-saarland.de" (IP 134.96.85.104): it consists of the host label "ecolotrain" and the domain name label "uni-saarland.de", where "de" is the so-called top-level domain.
Address resolution
So what happens when you request the eCoLoTrain webpage by pointing your browser to http://ecolotrain.uni-mainz.de/en? As you saw from the previous question, computers work with numbers only, so there has to be a mechanism to translate the hostname into its IP address in order to get the web page from the server. This is done by the so-called Domain Name System (DNS).
Why is this information important for translators and translation teachers?
It is important for translators and translation teachers to know what hostnames and domain names are, since these can offer important information on the origin, quality and reliability of documents found on the Internet and the information contained in them. If you are checking your German translation of an English legal term on the Internet and your translation is targeted at the German market, you would not necessarily trust results coming from Austrian or Swiss web pages, if you know that these countries have different legal systems.