An IDN homograph attack registers an internationalized domain name (IDN) built from homoglyphs — Unicode characters from other scripts that look identical to Latin letters — so the domain appears visually indistinguishable from a trusted brand.
Because the DNS encodes Unicode labels to ASCII via Punycode, an all-Cyrillic spelling of a brand registers as an innocuous xn-- string while rendering, in some contexts, as the real brand name.
Modern browsers defend against this by showing the xn-- form when a label mixes scripts or trips confusable rules, but the protection is uneven: single-script spoofs can still render, and email clients, chat apps, and link previews are far weaker. See the guide on homoglyph and IDN lookalike domains.