Negative numbers are values less than zero, represented with a minus sign (-). They are used to indicate a deficit or a loss, such as owing money or measuring temperatures below freezing. In mathematics, negative numbers extend the number line to the left of zero, allowing for a complete set of integers that includes both positive and negative values. Negative numbers are essential in various fields, including finance, where they represent debts, and science, where they can indicate temperatures below zero degrees. They also play a crucial role in algebra, helping to solve equations and understand relationships between different quantities.