Task queues are used as a mechanism to distribute work across threads or machines. The task is appended to the queue that calls task queue. Dedicated worker processes constantly monitor task queues for new work to perform.
Celery communicates via messages, usually using a broker to mediate between clients and workers. To initiate a task the client adds a message to the queue, the broker then delivers that message to a worker.
A Celery system can consist of multiple workers and brokers, giving way to high availability and horizontal scaling.