What exactly are the market makers in level 2 data? And what is there relation to the exchanges?

I'm sorry if this is the wrong sub for this, but I don't know where else to post it. I know level 2 shows the bid and offer of Market Makers for a particular stock, but how do these MMs relate to the exchanges? For example, one of the MMs I have seen is NYSE.

Submitted July 21, 2014 at 07:45PM by suck_dees_nuts http://ift.tt/1wSKGD1