Homoglyph

In orthography and typography, a homoglyph is a glyph that is used for either of a pair (or more) of distinct graphemes, or even a glyph whose shape appears identical or very similar to the glyph used for another grapheme. The designation is also applied to sequences of characters sharing these properties.

Examples of homoglyphic letters may be drawn from the Cyrillic and Latin alphabets. For example, a typical representative glyph for the Cyrillic letter Es is С, which is rarely distinguished from the glyph for the Latin letter C in the same typeface (or computer font). An extreme example is the hyphen-minus (-), which is widely used outside professional typography for any of hyphen, minus or en dash. Among digits and letters, the digit 1 (one) and the lowercase letter l ('ell') are always encoded separately but in many typefaces are given very similar glyphs. The same issue arises with the digit 0 (zero) and capital O ('oh'). Virtually every example of a homoglyphic pair of characters can potentially be differentiated graphically with clearly distinguishable glyphs and separate code points, but this is not always done. Typefaces that do not emphatically distinguish the one/el and zero/oh homoglyphs are considered unsuitable for writing formulas, network addresses, source code, IDs and other text where characters cannot always be differentiated without context.

In 2008, the Unicode Consortium published its Technical Report #36 on a range of issues deriving from the visual similarity of characters both in single scripts, and similarities between characters in different scripts.