Maker and Taker Fees
Exchange fees that charge less to orders which wait in the book and more to orders that trade immediately against them.
An order that rests and adds liquidity is a maker order; one that executes on arrival and removes liquidity is a taker order. Venues charge takers more, and some pay makers a rebate, because resting orders are what make the venue tradable. Fee schedules are usually tiered by a customer's trailing volume, so large participants pay materially less per trade than retail accounts. On an automated market maker there is no maker and taker distinction: every swap pays the pool's swap fee, which goes to liquidity providers rather than to a company.
In practice
A limit order placed away from the market and later filled is charged the maker rate, while the same order priced to execute at once is charged the taker rate.
The common misunderstanding
Maker status is decided by outcome, not intent: a limit order that executes the instant it arrives is charged as a taker order.