MCCXC is a Roman numeral that represents the number 990. In this numeral system, "M" stands for 1000, "C" stands for 100, and "X" stands for 10. The placement of the letters indicates subtraction and addition; thus, MCCXC can be broken down as 1000 (M) + 100 (C) + 100 (C) - 10 (X) - 10 (X), 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. For example, the year 1990 can be represented as MCMXC in Roman numerals, showcasing the versatility of this ancient numbering system.