Celery is a distributed task queue. It was first created for Django, but is now usable from Python. It can also operate with
other languages via HTTP+JSON. It is used for executing tasks asynchronously, routed to one or more worker servers, running
concurrently using multiprocessing. It is designed to solve certain problems related to running websites demanding high-availability and performance.

It is perfect for filling caches, posting updates to twitter, mass downloading data like syndication feeds or web scraping. Use-cases are plentiful. Implementing these features asynchronously using celery is easy and fun, and the performance improvements can make it more than worthwhile.