What are 'Master Royalties' in Marketplace?

Master Royalties cover Mechanical, Performance and Synch Royalties. 

As a Seller, when you choose a percentage on Master Royalties, this means you want to keep/retain that percentage of the Master Royalty. If you choose 30%, that means you would keep 30% of the Master Royalty and the buyer would keep 70%.

As a Buyer, the percentage shown is what percent of the Master Royalty the Seller wants to keep/retain.