This document discusses HBase, an open-source, distributed database system built on Hadoop. HBase is used for real-time big data applications and can store massive amounts of data from terabytes to petabytes. It is built for low latency operations on large tables containing billions of rows and millions of columns through features like random read/write access and linear scalability. The document compares HBase to other databases and explains why it is suitable for applications needing fast access to huge amounts of data.