I' is the Roman numeral for the number 1. It is the simplest and smallest of all Roman numerals. It is used in many contexts including dates, titles, and measurements. In dates, it is often used to denote the first month of the year, January. In titles, it is often used to denote a person's rank or status, such as Pope or Emperor. In measurements, it is often used to denote units of measurement, such as inches or feet.