What is an IDN ?
IDN stands for Internationalized domain name.
internationalized domain name (IDN) is an Internet domain name that (potentially) contains non-ASCII characters. Such domain names could contain letters with diacritics, as required by many European languages, or characters from non-Latin scripts such as Arabic or Chinese. However, the standard for domain names does not allow such characters, and much work has gone into finding a way around this, either by changing the standard, or by agreeing on a way to convert internationalized domain names into standard ASCII domain names while preserving the stability of the domain name system.
IDN has, by the standards of the Internet, a long history; it was originally proposed in 1996 (by M. Duerst) and implemented in 1998 (by T.W.Tan et al). After much debate and many competing proposals, a system called Internationalizing Domain Names in Applications (IDNA) was adopted as the chosen standard, and is currently, as of 2005, in the process of being rolled out.
source : wikipedia