HBase is a NoSQL database modeled after Google's Bigtable. It provides a distributed, scalable, big data store. Key features include horizontal scaling, reliability, column orientation, high performance random reads/writes, and seamless integration with Hadoop. Data is stored in tables containing rows, column families, and columns. The system is comprised of clients, Zookeeper, masters, region servers, and HDFS for data storage. Region servers handle read/write operations on regions, while masters manage region assignment and load balancing.