What is dot in i?

A dot in the letter "i" is called a tittle. It is a small mark that is commonly used in punctuation, particularly in the English language. The tittle was originally used in medieval scripts to distinguish the letter "i" from other similar looking letters such as "l" or "j". In modern typography, the tittle is typically used as a simple and consistent way to indicate the letter "i", although it may be omitted in certain situations such as stylized or decorative fonts.