"XCIX" is a Roman numeral that represents the number 99. In the Roman numeral system, letters are used to signify values, with "X" representing 10 and "C" representing 100. The "IX" part indicates 9, so when combined, "XCIX" means 100 minus 1, which equals 99. Roman numerals are often used in various contexts, such as in the naming of monarchs and popes, or to denote the chapters of books. For example, King Henry IX would be the ninth king named Henry, while Super Bowl IX refers to the ninth championship game in American football.