Nothing. There is no difference. 

Industrial Hemp refers to Cannabis sativa plant that has less than 0.3% THC by weight. 

In the Industrial Hemp Regulations, industrial hemp includes Cannabis plants and plant parts, of any variety, that contains 0.3% tetrahydrocannabinol (THC) or less in the leaves and flowering heads. 

When the Cannabis plant has less than 0.3% THC, the Farm Bill says it is Industrial Hemp and therefore legal to sell.