The document discusses the key components of Hadoop including the NameNode, DataNodes, JobTracker, TaskTracker, and SecondaryNameNode. The NameNode manages the file system metadata and keeps track of where data is stored across the DataNodes. The DataNodes store the actual data blocks. The JobTracker manages jobs by determining which TaskTrackers on the slaves will execute tasks. The SecondaryNameNode helps if the NameNode fails by providing additional backup of metadata.