prime number

A prime number is a number with only 2 factors. 

eg 7 is a prime number as it only has two factors (1 ✕ 7)

A composite number is a number with more than 2 factors.

eg 8 is a composite number as it has more than 2 factors (1 ✕ 8 and 2 ✕ 4) 

A prime factor is a number that is a factor of another number and also a prime number.

Example

The factors of 20 are: 1, 2, 4, 5, 10 & 20.

The prime factors of 20 are 2 and 5.

A factor tree (shown below) is sometimes a useful way to find prime factors of a number.

Example

The numbers 2 and 5 are the prime factors of the number 20 (2 ✕ 2 ✕ 5 = 20).