In mathematics, the word sign refers to the property of being positive or negative. Every real number that is non-zero is either positive or negative, and therefore has a sign. Zero itself is without a sign, or signless. In addition to putting signs into real numbers, the word sign is used throughout mathematics to indicate parts of mathematical objects that mean positivity and negativity. Usually, if numbers are seen without a sign, they are seen as a positive number. Otherwise, a minus sign "formula_1" is appended before the number to indicate that the number is a negative of another number.