An internationalized domain name (IDN) is an Internet domain name that (potentially) contains non-ASCII characters. Such domain names could contain letters or characters from non-Latin scripts such as Chinese (like the domain hosting this blog), Arabic, Korean etc.
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.
In IDNA, the term internationalized domain name means specifically any domain name consisting only of labels to which the IDNA ToASCII algorithm can be successfully applied. (For the meaning of ‘label’ and ‘ToASCII’, see the Wikipedia sections ToASCII and ToUnicode under Internationalized Domain Name.)