The dot over the lower case "i" or "j" is known as a "tittle."

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That tiny dot above lower case "I" and "j" letters has an actual name: tittle. It is thought that the phrase "to a T" is actually derived from the phrase "to a tittle"—a phrase that was used in the same sense dating back to the early 17th century. (The first recording of the phrase is in the 1607 play Woman Hater by Francis Beaumont and John Fletcher, in which the line reads, "I'll quote him to a tittle.")