Hadoop is a system for processing large amounts of data using MapReduce and HDFS. HDFS is the storage component that splits files into blocks and stores multiple copies for reliability. MapReduce is the processing framework where mappers process key-value pairs in parallel and reducers aggregate the outputs. While Hadoop can process huge datasets, other systems like Pig, Hive, HBase, Accumulo, Avro, ZooKeeper, and Flume provide additional functionality for tasks like SQL queries, real-time processing, coordination, serialization, and data aggregation.