A composite number is a positive integer that has a factor other than 1 and itself. For instance, 6 is a composite number because:
 it is positive
 it has a factor other than 1 and itself (both 2 and 3 are factors of 6)
If you are familiar with prime numbers, then you should recognize that a positive integer is either prime or compositethese two terms are mutually exclusive.
Examples of Composite Numbers
 4
 4 is composite because 2 is a factor
 8
 8 is a composite number because it has 4 and 2 as factors
Non examples of Composite Numbers
 5

5 is not a composite number because its only factors are 1 and itself (5). 5 is, however, a prime number.
 2

2 is not a composite number because its only factors are 1 and itself (2). 2 is, however, a prime number. 2 is also the even number that is not composite. Every other even number is indeed a composite number.
 7

7 is not a composite number because its only factors are 1 and itself (7). 7 is, however, a prime number.