It is domain name with the ending Ninja after the dot. Ex. warrior.ninja. Anyone who is brave enough can get one. It is a great domain name for anyone that wants to spice the name up.
This TLD was delegated on 28 of December, 2013, but became available for public the next year - 28 May 2014. At the moment there are more than 30,000 registered domains using .ninja. If you want to get more in-depth details about this TLD read ICANNWiki. It is a great resource.
More about this TLD
The name can be used by anyone. It is not limited. Dot Ninja fits a lot of businesses such as e-commerce, sport gyms, SEO agencies and much more. Just turn on your imagination. Furthermore, it is very easy to remember and of course sounds cool. The usability is almost limitless.
Finally, we were able to find a lot of free domain names using the .ninja ending. So if .com or .net is already taken, this is a great chance to find the one you need.
If you are considered that it will not rank on Google or Yahoo Search, do not worry. This TLD works nicely as any other domain.
It is a great name! Check if the one is available and grab it.