Redis is an open-source, networked, in-memory database that is used as a database, cache, and message broker. It is used as a database for caching and storing data, to boost the performance of interactive applications such as real-time analytics or gaming. It helps to process messages in a background processing system more efficiently. Also, it is a key-value store that is more flexible than traditional databases because the data structure is simpler and keys can contain more complex data types. 

Why Redis? 

• Simple database that stores data in a key-value pair with a built-in set of atomic operations on the values. 
• Few data structures, such as strings, hashes, lists, sets, and sorted sets. 
• Supports different kinds of value types, including strings, hashes, lists, sets, and sorted sets. 
• Non-relational database as it doesn’t support joins or relations. 
• It is an in-memory database, which means it speeds up operations and reduces latency. 
• Supports master-slave replication and persistence through an append-only file. 
• In-memory databases like Redis are useful for speeding up transactional systems, caching, and queueing.