Over the last month or so, new gTLDs (generic top level domains) have been added to the root zone by ICANN. This is the beginning of a process of adding a couple hundred new gTLDs which ICANN colleted applications for last year.
To get a full list of current valid gTLDs see http://newgtlds.icann.org/en/program-status/delegated-strings
It is up to the individual registrars who received the gTLDs to decide how to use them. Some are limited to particular organizations. Others are already available to the public for pre-registration.
This is important if you are doing more detailed input validation on domain names, for example to validate e-mail addresses. For example, the longest name I was able to spot was ".INTERNATIONAL" .
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