Can someone explain to me about a stock "Market Maker"?

[askwdc]

I have read this off of investopedia.com. I just want to see other takes/views on it. I do not firmly grasp the concept.

Market Maker

A broker-dealer firm that accepts the risk of holding a certain number of shares of a particular security in order to facilitate trading in that security. Each market maker competes for customer order flow by displaying buy and sell quotations for a guaranteed number of shares. Once an order is received, the market maker immediately sells from its own inventory or seeks an offsetting order. This process takes place in mere seconds.
The Nasdaq is the prime example of an operation of market makers. There are more than 500 member firms that act as Nasdaq market makers, keeping the financial markets running efficiently because they are willing to quote both bid and offer prices for an asset.