Redis is an in-memory data structure store that can be used as a database, cache, and message broker. It stores all data in memory rather than on disk which makes it extremely fast. Redis supports a rich set of data structures such as strings, hashes, lists, sets, sorted sets with range queries, bitmaps, hyperloglogs, and geospatial indexes with radius queries. Redis also provides various features like transactions, pub/sub messaging, Lua scripting, and LRU eviction of keys to manage the dataset. Redis is a NoSQL database and falls under the category of key-value stores.