What is a profit margin?

A profit margin is the percentage of total ada rewards that the stake pool operator takes before sharing the rest of the rewards among all the delegators to the pool. A lower profit margin for the operator means they are taking less, which means that delegators can expect to receive more of the rewards for their delegated stake. A private pool is a pool with a profit margin of 100%, meaning that all the rewards will go to the operator and none to the delegators.