The document discusses the key components of Hadoop including the NameNode, DataNodes, JobTracker, TaskTracker, and SecondaryNameNode. The NameNode stores metadata for HDFS and tracks where data is stored across DataNodes on the slaves. The JobTracker schedules jobs on TaskTrackers across the slaves. The SecondaryNameNode assists the NameNode in the event of failure. Hadoop uses a master-slave architecture with the NameNode and JobTracker on the master and DataNodes and TaskTrackers on the slaves.