What is a master and data node?

[tomer (tomer zaks)]

I will be happy if some one can explain me what is a master and data node?

P.S.
I read the guide on nodes but still am confused.

[warkolm (Mark Walkom)]

A data node holds shards that make up the indices.

A master node makes sure the cluster is stable by taking part in quorum decisions and updating cluster state.

[tomer (tomer zaks)]

Thanks @warkolm,

Can a master node also be a data node?

Just to be sure:
From my understanding a data node is basically an object that holds the data (by holding shards that hold data). While the master node is the same type of object that instead of holding data it is in charge of managing the whole cluster. Is this true?

[warkolm (Mark Walkom)]

By default a node is a master (eligible) and a data node.

Your summary is correct.