Answer:
It means that you are done.
Explanation:
When you are trying to find factors of a number or an algebraic expression, you must keep on factoring until you have all PRIME factors. PRIME factors cannot be further factored. So that means you are done factoring.
example: (a number)
6
factors: 2 and 3
2 and 3 are prime they can't be factored anymore so you have completely factored 6.
example: 20
factors: 4 and 5
5 is prime but 4 is not, so you can factor it more.
4 is 2×2
So 20 factored is 2×2×5
Or algebra example:
Factor x^4 - 81
factors: x^2 - 9 and x^2 + 9
x^2 + 9 cannot be factored more (prime) but x^2-9 can. Its x-3 and x+3.