The number -12 belongs to the set of integers.
Integers are the set of whole numbers (positive numbers including zero) and their negatives. In other words, integers include all positive numbers, negative numbers, and zero. The set of integers can be represented as {..., -3, -2, -1, 0, 1, 2, 3, ...}.
Whole numbers are the set of non-negative integers, including zero. In other words, whole numbers are the positive numbers and zero. The set of whole numbers can be represented as {0, 1, 2, 3, ...}.
Natural numbers are the set of positive integers, excluding zero. In other words, natural numbers are the positive numbers only. The set of natural numbers can be represented as {1, 2, 3, ...}.