Maker
A trader whose limit order rests in the order book, adding liquidity and typically earning a fee rebate on maker-taker exchanges.
A maker is a market participant who places a resting limit order that is not immediately filled. Their order sits in the book and makes liquidity available for others.
On maker-taker fee schedules, makers are rewarded with a rebate for providing this liquidity, because exchanges benefit from having a rich, tight order book. The rebate is typically a fraction of a cent per share or a few basis points per trade.
Understanding maker vs. taker status is essential for high-frequency and active traders where routing decisions meaningfully affect net P&L.