Riak is a distributed NoSQL database designed for high availability and fault tolerance. It uses a key-value store model, allowing users to store and retrieve data efficiently across multiple nodes. This architecture ensures that even if some nodes fail, the system continues to operate without losing data. One of the key features of Riak is its ability to scale horizontally, meaning users can add more servers to handle increased loads. It also supports eventual consistency, which allows for faster write operations while ensuring that all copies of the data will eventually synchronize.