Redis, which stands for Remote Dictionary Server, is a fast, open-source, in-memory key-value data store (or data structure store) for use as a database, cache, message broker, and queue.
Amazon Redis is a fully managed in-memory data store and thus on-demand sizing. It powers real-time applications with sub-milliseconds latency. As per AWS portal, All Redis data resides in-memory, in contrast to databases that store data on disk or SSDs. By eliminating the need to access disks, in-memory data stores such as Redis avoid seek time delays and can access data in microseconds. Redis features versatile data structures, high availability, geospatial, Lua scripting, transactions, on-disk persistence, and cluster support making it simpler to build real-time internet scale apps.