Differentiate between Taker and Maker Fees in a Futures Market.
Taker fees are paid by traders who place orders that are immediately filled against existing orders on the order book, thus 'taking' liquidity. Maker fees are paid by traders who place limit orders that add liquidity to the order book, which are not immediately filled.
Exchanges often charge lower maker fees, or even offer rebates, to incentivize liquidity provision.