Although we're unsure at the moment, it would be reasonable to assume that the three numbers stand for different storage capacities, such as 32 / 64 / 128 GB variants. (androidauthority.com)
While you and I will make the same amount of milk within a 24 hour period, we actually have different storage capacities in our breasts. (themilkmeg.com)
Women also have different storage capacities within their breasts. (themilkmeg.com)