Celery is a distributed task queue system that allows putting tasks in a task queue to be processed asynchronously by worker processes or threads. It supports common features like events, workflows, rate limits, retries, and routing. Celery can use many different brokers like RabbitMQ, Redis, MongoDB, and SQL databases to store tasks and results. It is extensible and works well for asynchronous tasks like emails, image processing, data imports, and API calls.