A symbol used to denote a number. The Roman numerals I, V, X, L, C, D, and M represent 1, 5, 10, 50, 100, 500, and 1000 in the Roman number system. The Arabic numerals 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 are used in the Hindu–Arabic number system to give numbers in the form generally familiar today. See number systems.