This refers to the number of unique concept designs that you'll get to choose from. With custom logos you get:
3 unique concept designs (Budget package)
15 unique concept designs (Silver package)
30 unique concept designs (Gold Package)
Unlimited unique concept designs (Platinum Package)
With the pre-designed logos you can pick any of the logos in the pre-designed logos section. There are thousands of unique designs. Yes, they really are unique and each one is sold only once. The only catch is that they are not custom designed to your specifications - made up for by the fact that you get to see it before you pay for it.
No matter what you order, you receive unlimited alterations to your chosen design.