Hadoop is an open-source programming framework developed to store and process massive amounts of data. It operates by distributing data across many machines and having each machine process the data at the same time to enable Big Data analytics. One of the key differentiators of Hadoop from other data storage solutions like relational databases is that it can process unstructured data in addition to structured data.
Hadoop is similar to Cassandra in that they both address ways to store massive amounts of data. Hadoop differs from Cassandra, however, in that it does not process data as fast as Cassandra and consequently is better suited for analytics operations that are more time-intensive.