Composite Numbers
What Is a Composite Number?
A composite number is a number that can be divided exactly by at least one number that is not itself or 1.
This means a composite number is any number (other that 1) that is not a prime number.
For example,

4 is a composite number. It can be divided exactly by 1, 2 and 4.
4 is a composite number because it can be divided by 2 (which is not 1 or 4 itself).

5 is not a composite number. It can only be divided exactly by 1 and 5.
5 is a prime number because it can only be divided by 1 and 5 itself.
Dictionary Definition
The Oxford English Dictionary defines a composite number as "a number which is the product of two or more factors, greater than unity."
The Composite Numbers
The composite numbers are:
In a number square, the composite numbers are shaded below:
Note: This is the exact inverse of the prime numbers in a square. If this number square is overlaid with that of the prime numbers, all numbers (apart from 1) would shaded.