A negative number is a value that is less than zero. It is represented with a minus sign (-) in front of the number, such as -1, -2, or -10. Negative numbers are used in various contexts, such as measuring temperatures below freezing or representing debts in finance. In mathematics, negative numbers are part of the set of integers, which includes both positive numbers and zero. They can be used in calculations, such as addition and subtraction, where adding a negative number is equivalent to subtracting its positive counterpart.