Data push is at the core of realtime.  Simply speaking, it is when the given data transaction is initiated by the publisher or generator, instead of by the receiver or client.  A good way to think about this is with the publish/subscribe model, whereby the a client “subscribes” to various information “channels” provided by a server; whenever new content is available on one of those channels, the server pushes that information out to the client.

Resources

Push technology