IDN is short for Internationalized Domain Names.
Previously, as a rule, all domain names contained only letters from ASCII encoding, numbers from 0 to 9 and the hyphen, that is, used only Latin letters. However, in 2003 a specification was issued that allowed the use of most Unicode characters in domain names. This made it possible to register domains not only in English, but also to use other languages in domain names. Not all domains yet support this specification, but today most popular domain zones already support IDN. So you can register the name in your native language. The use of such domains is possible thanks to punycode conversion of IDN domains to ASCII encoding. All systems store names in this format. But already most browsers, mail clients, ftp clients support IDN. Therefore, in most cases you do not need to recode your name in punycode to open the site, but rather use the name in the language in which it was registered.