What is Redis and how is it used in PHP?

Redis is an in-memory data structure store used as a cache, message broker, and session store. In PHP applications, it is commonly used for: caching (storing frequently accessed database results), session storage (faster and more scalable than file-based sessions), queue backends (Laravel queues with the Redis driver), rate limiting, and pub/sub messaging. Connect using the predis/predis Composer package or the phpredis C extension (faster). In Laravel, configure Redis in config/database.php and use it with Cache::remember(), Session::driver("redis"), or the Queue system. Redis is significantly faster than database-based caching because all data lives in RAM.