I have read before on previous posts (and I think it was in the book too) about eating 80/20. Eating primal 80% of the time. What does that mean really?

Does it mean 20% of the time we can have the sweat potato's, brown/wild rice, fruit (which I am really missing a lot...I want to eat everyday), Cheese, Yogurt, or Cream?

Or does it mean that 20% of the time you do not eat primal and you can have grain or beans?