The small dot placed above a lowercase “i” or “j” is called a tittle. It is a specialized diacritic that forms part of these letter shapes in many Latin-alphabet writing systems.
The word is uncommon in everyday speech, but it appears in the familiar expression “every jot and tittle,” meaning every tiny detail. That phrase comes from the King James Bible, Matthew 5:18, where “jot” and “tittle” describe the smallest marks of written law. The biblical Greek uses iota and keraia, whose exact meanings have been debated by scholars.
A tittle is not the same as an umlaut, which marks a vowel change in languages such as German, or a serif, which is a finishing stroke on a typeface. “Diacritic” is a broader category: the tittle is one particular kind of diacritic. In most Latin-based orthographies, the dot disappears when a mark is placed directly above the i or j, as in í or ĵ.
Turkish demonstrates why the dot matters. Its dotted and dotless forms—İ/i and I/ı—represent different letters and sounds, rather than merely different type styles.