A market maker is a broker-dealer firm or a registered individual that will hold a certain number of shares of a security in order to facilitate trading.
There could be as many as 50 market makers for one particular security, and they compete for customer order flows by displaying buy and sell quotations for a guaranteed number of shares.
The market maker spread refers to the difference between the amount a market maker is willing to pay for a security and the amount that the other party is willing to sell it.