What is the primary characteristic of a negative number?

A negative number is defined primarily by its ability to represent a value that is less than zero. In number theory and real-world applications, negative numbers are used to signify deficits, temperatures below freezing, financial losses, and other scenarios where a value is below a defined baseline, which is zero.

The distinction is particularly important in various fields such as mathematics, physics, and economics, where understanding the implications of negative values is crucial for proper analysis and interpretation. For example, in a financial context, a negative number indicates a debt or loss, while in temperature, it indicates conditions that are below the freezing point.

The other options do not accurately capture the essence of negative numbers as they either mischaracterize their value in relation to zero, incorrectly limit them to integers, or suggest they are not part of any number system, which is not true; negative numbers can exist in various number systems, such as integers, rational numbers, and real numbers.