A placeholder is a number that, as the name implies, holds a place. Initially, various cultures used a placeholder—often a dot or a space—to show an empty spot or place not used in a numeral (or other way of counting). This was in place of what we now call a zero (0), a symbol that is not only a placeholder, but an essential number in our numeration system. (For more about the evolution of the symbol zero [0], see “History of Mathematics.”)