A domain name is is a website address, such as google.com or wikipedia.org. The letters that you see after the dot refer to the top level domain.
Now for those who are interested in the Ethereum cryptocurrency, an ETH domain is now available.
As an example, some of the Dot ETH domains that are currently available for bidding and sale on Sedo include the following:
There are hundreds of other ETH domains currently on the list.
If you want to register your own ETH domain name, you can go to ens.domains