Characters (or words) from different scripts that look so similar to one another that it is difficult to tell them apart just by looking. The homoglyphs below are two different characters from two different scripts, or alphabets. They have different Unicode numbers but look identical.
Cyrillic character: a Unicode number 0430
Latin character: a Unicode number 0061
Domain name that contains characters from non-ASCII character sets. These include characters with accents, cedillas and ogoneks.
Examples include the Swedish å, the German ü, the Romanian ș and characters from the Bulgarian and Greek alphabets as a whole.
IDNs are particularly important for .eu as the European Union has 27 Member States and 23 official languages. Many of these languages use non-ASCII characters in their alphabets.