It means that offering the tickets below that price won’t pay the direct costs for the ticket and in respect of the rules of the game it is not allowed to do so as this would be price-dumping.
If I have a route where the income I receive from passenger operations fully funds the cost of operating the aircraft from point A - B, can I not lower my cargo price below the published minimum price to fill my empty cargo holds? As long as the price for cargo is above the associated handling fees for cargo I am covering my costs of delivering cargo from point A - B.