What did mean by Data-Node?

Data-Node stores information in HDFS; it is a node where the real information resides in the document. Each data node sends a pulse message to notify that it is alive. If the name-node does not get a message from data-node for 10 minutes, it is considered to be dead or out of place and begins replication of obstructs that were facilitated on that information node with the end goal that they are facilitated on some other information node. A Block-Report consists of the list rundown of all blocks on a Data-Node.