CMXC is a Roman numeral that represents the number 990. In this system, "C" stands for 100, "M" for 1000, "X" for 10, and "V" for 5. The combination of these letters indicates that 900 (CM) is added to 90 (XC), resulting in 990. Roman numerals are often used in various contexts, such as in the naming of monarchs and popes, or to denote the year of publication in books. Understanding Roman numerals, including CMXC, can be helpful in reading historical texts or interpreting dates in classical literature.