A negative integer is a whole number that is less than zero. These numbers are found on the left side of the number line and are represented with a minus sign (-). Examples of negative integers include -1, -2, -3, and so on. They are used in various mathematical contexts, such as representing debts or temperatures below zero. Negative integers are part of the set of integers, which also includes positive integers and zero. In mathematics, they play a crucial role in operations like addition and subtraction. For instance, adding a negative integer to a positive integer can decrease the overall value, illustrating how they interact within the number system.