Hadoop is an open-source software framework that allows for the distributed processing of large data sets across clusters of computers using simple programming models. It is designed to scale up from single servers to thousands of machines, each offering local computation and storage. Hadoop automatically manages data replication and platform failure to ensure very large data sets can be processed efficiently in a reliable, fault-tolerant manner. Common uses of Hadoop include log analysis, data warehousing, web indexing, machine learning, financial analysis, and scientific applications.