TL;DR A market maker is a firm that continuously offers to both buy AND sell a stock, earning the small gap between those prices (the spread) in exchange for making sure your order fills instantly.
The plain-English version
When you tap "buy," you're rarely matched with another human who happens to be selling that exact moment. Someone stands in the middle: the market maker, quoting both sides all day — "I'll buy at $99.98, I'll sell at $100.02."
That 4-cent gap is the spread — their compensation for always being there. Like a currency-exchange booth at the airport: always willing to trade either direction, always at prices that leave them a sliver.
Their goal isn't betting on direction — it's staying neutral, collecting spreads thousands of times a day, and hedging (often with options and offsetting stock positions — which is exactly how the mechanics behind gamma squeezes arise).
Why they exist
Without them, you'd wait for a matching human — minutes on popular stocks, days on small ones, at whatever ugly price desperation produces. Market makers are why modern stocks fill in milliseconds with penny spreads. Boring, load-bearing plumbing.
The controversies, honestly
Payment for order flow (PFOF): many "free" brokers route your orders to market makers who pay for them. It's how zero-commission trading is funded, it's disclosed, regulators watch it, and the debate over whether your fill price quietly suffers is legitimate and ongoing. Meme lore: market makers star as cartoon villains in every squeeze saga — manipulating everything, hunting your stop-loss personally. The mundane truth: they profit from volume and spreads, not from your specific downfall. Nobody needed a conspiracy to take the other side of a bad trade.
The common mistake
Believing "someone sold to me instantly" means "someone smart disagrees with me." Usually a machine served you liquidity, spread included, opinion not included.
Educational only — not investment advice. The house doesn't hate you; it charges everyone the same toll.