Well, it is "Internationalized Domain Name"
And I learned a bit about it in this blog article: "Scripts and Barriers"
Why should you know and why should you care ? This really is where our webbrowsing is going in the future! Though the opinions seem to vary, it appears that much of this will be implemented, in the name of protecting us from phishers and scammers.
You should at least be aware that it is coming soon, to a browser near you!