Internationalized domain name (IDN) homograph attack is way a thirdparty may confuse users exploiting the fact that many characters may look alike. For example urls "https://bank.com" and "https://bаnk.com" are look as the same, but actually first url contains latin "a", the second cyrilic "а" which looks alike latin. This characters are called "homoglyphs". You may find more homoglyphs at http://www.irongeek.com/homoglyph-attack-generator.php .
IDN can be represented as unicode url or punycode.
Basically you can't register domain names with homoglyphs. Try to register "bаnk.com" and request will be rejected, because this name contains cyrilic "а". IDN registration policy not allow to mix latin and cyrilic letters. More details about restrictions you can find here and at iana.org.
In IDN latin table (which represent permitted code points (letters) allowed for Internationalised Domain Name registrations) exis…