Redis is an in-memory, single-threaded, open-source NoSQL datastore that offers high performance and flexibility. It's often used as a cache or lightweight message broker due to its ability to handle over 100k SETs (writes) and 81k GETs (reads) per second. Unlike SQL databases, Redis doesn't implement ACID-supporting database schemas such as tables and columns. Instead, it offers a range of data types including strings, lists, sets, sorted sets, hashes, bitmaps, and hyperloglogs. These features make Redis an excellent choice for fast changing stores and caches.