A FACTOR is a number that divides exactly into another number.
A PRIME number is one that only has two factors, itself and 1.
A PRIME FACTOR is a factor that also happens to be a prime number.
The number 42 has factors 42, 21, 14, 7, 6, 3, 2 and 1.
Which of these are PRIME FACTORS?
The only prime numbers in this list are 2, 3 and 7.
Remember that 1 is not a prime number.
So the PRIME FACTORS of 42 are 2, 3 and 7.