Oh sorry, I didn't realise that you meant that. IDNs are simply domains that use non-ascii characters. As for why they exist, they serve languages which use an extended character set, such as latin languages which usually use accents (à, é, è, î, etc.). It dosen't really make sense to leave out the accents when writing as they are actually a part of the word (and define the meaning and prononciation). So in order to include them in the Domain Name System, which is ascii based, a system was developed (IDNA) to allow them to be translated to ascii.
Besides their usefulness in helping to 'conform' the internet to non-english languages, IDNs also affords flexability to the Domain Name System by allowing for new symbols to be added (such as €
.
One thing that I should probably add is that since you can mix scripts and character sets when forming a domain, a lot of IDN domains are used for spoofing. If you use Gmail and Paypal, you probably receive warnings that messages that appear to be from PayPal.com are not. This is because the sending is actually using "pаypal" with a cyrillic letter 'a' rather than a latin letter 'a', but they look the same.
Quote:are they also under ICANN??
yes.. and they are just like ordinary domains, except that they must first be translated in to ascii.