A numeral is a symbol or group of symbols, or a word in a natural language that represents a number. Numerals differ from numbers just as the word "rock" differs from a real rock. The symbols "11", "eleven" and "XI" are different numerals, all representing the same number. This article tries to explain the different systems of numerals. Greek numerals and Roman numerals are among the systems that were long used, before the Hindu–Arabic numeral system largely replaced them.