A deficient number is a positive integer that is greater than the sum of its proper divisors, excluding itself. For example, the number 8 has proper divisors 1, 2, and 4, which add up to 7. Since 7 is less than 8, the number 8 is classified as deficient. Deficient numbers are part of a broader category of integers known as abundant and perfect numbers. An abundant number has a sum of proper divisors greater than itself, while a perfect number has a sum equal to itself. Understanding these classifications helps in the study of number theory and its properties.