Redis, also known as the Remote Dictionary Server, is NoSQL server software first released in 2009. It is a key-value store that serves data structures to applications. It can serve strings, lists of strings, sets of strings, sorted sets of strings, and hash tables. Because Redis stores its data in memory, it has performance benefits over traditional databases that must write all data to disk before altering the database contents. It's not ideal for data such as financial transactions but excels at things like persistent session information and user messaging.