Well to put it simply, a master node is a full node which rewards node operators for performing the core consensus function of running a blockchain. Due to the nature of how full nodes computers work and the financial constraints involved in running them, a lot of people will want to reduce the number of full node computers they have connected to a blockchain and this will in turn lead to problems like slow transaction processing times and congestion of the particular blockchain.

Now this is where master nodes come into place, they act as full nodes and the people operating them are financially rewarded for their services.

And I don't think I am, I know Dash uses master nodes and I don't have and I don't have any Dash.