IDN means Internationalized Domain Name; it’s an internet domain name that contains 1 or more non-ASCII characters (or chars).

The ASCII chars available to register a domain name are:
0 1 2 3 4 5 6 7 8 9 – a b c d e f g h i j k l m n o p q r s t u v w x y z

The ASCII domains don’t contain letters required by many European languages or chars from non-Latin scripts like Chinese, Indian, Japanese, Arabic, etc. So IDN chars provide a way for users to access Web sites in their local language. In such a way, IDNs transform Internet into a multilingual tool. Note that the IDN system can use the specific characters of more than 350 different languages.
IDNs allow companies to create domain names that are not only meaningful and effective in the local language, but also function globally. Internationalized Domain Names are easy to remember for local people and make the Web more flexible to better fit the needs of companies and their customers.
Anyway, to preserve the stability of the domain name system, each Internationalized Domain Name can be converted to the corresponding ASCII version, which is graphically completely different (the so called punycode version).

To be able to use IDNs as web addresses, the browser must be capable of converting the IDN entered in the address bar to the corresponding standard string.
The browsers which include IDN support are:
Mozilla version 1.4 and above;
Netscape Navigator version 7.1 and above;
Firefox version 0.8 and above;
Konqueror KDE 3.2 and above with GNU IDN library;
Opera version 7.11 and above;
Safari version 1.2 (v125) and above;
Microsoft Internet Explorer version 7.0; the version 5.0 and above, can be made IDN capable by installing the i-nav plugin by VeriSign. IE 6 produces errors despite plugin.