Hadoop is an open-source framework for distributed storage and processing of large data sets. Key components include HDFS (storage), MapReduce (processing), YARN (resource management), and Hadoop Common (utilities). Its architecture follows a master-slave model with Master Nodes (NameNode, JobTracker) managing data and tasks, and Slave Nodes (DataNodes, TaskTrackers) storing data and performing computations. Hadoop is used in data warehousing, business intelligence, machine learning, and large-scale data processing, making it essential for big data applications.

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