Redis is an in-memory data structure store commonly used as a database, cache, and message broker. Its key mental model is that every key maps to exactly one data type, and commands are valid (or invalid) based on that type. Day-to-day success with Redis usually comes down to choosing the right structure (e.g., sorted sets for leaderboards, streams for event logs) and using safe key iteration (SCAN) plus explicit expiry (EXPIRE). Operationally, treat Redis as a long-running server you secure (ACL/TLS) and observe (INFO, SLOWLOG) rather than “just a library.”