market maker: a party that fulfills a stock order. Market makers include a retail broker (such as TradeStation), a stock exchange (e.g., NYSE or NASDAQ), or a clearinghouse firm. A market maker continuously posts both buy and sell prices for a stock, standing ready to trade so that other participants can transact instantly. They keep markets liquid by always being willing to take the other side of an order, and they earn money from the bid–ask spread.