Step 1: Recall price discrimination.
This means charging different prices for the same product. There are three degrees of it.
Step 2: Match the clue in the question.
Here different quantities sell at different prices, but anyone buying the same quantity pays the same price. So price depends on how much you buy, not on who you are.
Step 3: Name that case.
Charging by the quantity block, like bulk discounts, is second degree price discrimination.
Step 4: Rule out the rest.
First degree, also called perfect, charges each buyer the most they will pay. Third degree splits buyers into groups like students or seniors. Neither fits the clue.
Step 5: Conclude.
\[ \boxed{\text{second degree}} \]