A homoglyph is a character that looks like another character, or nearly the same, even though it has a different Unicode code point. In security, homoglyphs matter because a domain, username, file name, or message can be made to look familiar while still being technically different. For example, a spoofed hostname may swap one Latin letter for a similar-looking character from another script, making a phishing site seem trustworthy at a quick glance.
Homoglyphs are a core tool in typosquatting and brand impersonation. They can also interact with internationalized domain names, where browsers may render Unicode or fall back to Punycode depending on their spoof-detection rules. Defenders should compare suspicious names in both Unicode and ASCII forms, watch for mixed-script labels, and use tools that detect confusables or skeleton matches. The risk is not that the name is invalid, but that it is visually persuasive enough to bypass human attention.