Apache Cassandra is an open-source, distributed database management system designed to handle large amounts of data across many servers. It offers high availability and scalability, making it suitable for applications that require continuous uptime and the ability to grow seamlessly. Cassandra uses a unique data model based on a wide-column store, allowing for flexible data storage and retrieval. One of the key features of Cassandra is its ability to provide fault tolerance through data replication across multiple nodes. This means that even if some servers fail, the system can still function without losing data. Its decentralized architecture ensures that there is no single point of failure, making it a popular choice for big data applications.