A market maker is a firm or individual that stands ready to buy and sell securities at publicly quoted prices. Market makers profit from the small difference between buying and selling prices, called the spread. They improve liquidity by always being available to trade.
A market maker might offer to buy Apple stock at $150 and sell it at $150.10. When you buy shares, the market maker sells to you at $150.10, and when you sell, they buy from you at $150. This small $0.10 spread per share is their profit.
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