A system of numerical notations used by the Romans. It is an additive (and subtractive) system in which letters are used to denote certain ``base'' numbers, and arbitrary numbers are then denoted using combinations of symbols.
For example, the number 1732 would be denoted MDCCXXXII. One additional rule states that, instead of using four symbols to represent a 4, 40, 9, 90, etc., such numbers are instead denoted by preceding the symbol for 5, 50, 10, 100, etc., with a symbol indicating subtraction. For example, 4 is denoted IV, 9 as IX, 40 as XL, etc. However, this rule is generally not followed on the faces of clocks, where IIII is usually encountered instead of IV.
Roman numerals are encountered in the release year for movies and occasionally on the numerals on the faces of watches and clocks, but in few other modern instances. They do have the advantage that Addition can be done ``symbolically'' (and without worrying about the ``place'' of a given Digit) by simply combining all the symbols together, grouping, writing groups of 5 Is as V, groups of 2 Vs as X, etc.