Definition
A market maker is a participant that regularly quotes prices at which it is willing to buy and sell specified instruments.
In market context
Market makers can support continuous trading by committing capital and managing inventory while earning spreads or other compensation. Their quoted size, obligations, and protections depend on venue rules, and they can widen or withdraw quotes in permitted circumstances. A market maker may also be the counterparty to a customer trade, creating execution and conflict considerations that should be addressed by applicable best-execution duties.
Source
Use the primary source for fuller regulatory or market context.
