IDN abbreviation stands for Internationalized Domain Name. IDN defines a domain name containing national diacritical characters specific for particular language, for example: ą, ć, ę, ł, ń, ó, ś, ż, ź (Polish diacritics).
Through the possibility of registering domain names containing diacritics it is possible to use original sounding names. At present, müller.pl is not the same as mueller.pl.
Technically, an operation of IDNs is based on existence of two forms of the domain: an outer form - with the diacritics, and a technical form (inner) transformed by means of special algorithm (Punycode) into a form which can be input into DNS. The technical form begins with "xn--" prefix followed by a string of Latin characters.