Market maker

A market maker is a participant who continuously posts both buy and sell quotes for an asset, standing ready to trade from their own inventory. They earn the spread — the gap between bid and ask — and in exchange provide liquidity so everyone else can trade at reasonable prices throughout the session. Examples: Citadel and Virtu in US equities, Jump and Wintermute in crypto, and your broker's internal desk when you buy retail. The business only works at scale and speed, which is why modern market makers are essentially HFT firms. See bid-ask spread for how the economics actually work.