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 of 1, 2, and 4, which add up to 7. Since 7 is less than 8, the number 8 is classified as deficient. In contrast, a perfect number is one where the sum of its proper divisors equals the number itself, like 6, which has proper divisors 1, 2, and 3 that sum to 6. Another type, called an abundant number, has a sum of proper divisors greater than the number itself, such as 12.