#### Answer

A prime number has exactly two factors, while
a composite number has more than two.

#### Work Step by Step

Every natural number has factors: 1 and itself.
(The number 1 has only one factor, all others have at least two).
If a natural number has only these two factors, it is a prime number.
If it has factors other than these two, it is composite.
The lowest prime number is 2 (1 has only one factor, so it is not considered as prime).
Examples:
15 is a composite number because, besides 1 and 15, it has 3 and 5 as factors.
16 is a composite number because, besides 1 and 16, it has 2,4, and 8 as factors.
17 is a prime number, because the only factors it has are 1 and 17.
18 is a composite number because, besides 1 and 18, it has 2,3,6 and 9 as factors.
19 is a prime number, because the only factors it has are 1 and 19.