There are three sides to the cloud:
1. The authoring tool. I edit and update a feed. It contains a
element that says how a subscriber should request to notification of updates. 2. The cloud. It is notified of an update, and then in turn notifies all subscribers.
3. The subscriber. A feed reader, aggregator, whatever — that subscribes to feeds that may or may not be part of a cloud.
Old RSS push gets new momentum thanks to WordPress.com