To overcome the deficiency of having no mechanism for a server to independently push data to a client without a client first making a request, HTTP Long Polling was born. HTTP long polling is a technique where the client polls the server to request new information. This enables developers to build realtime applications, and pushes new data as it happens.
In this video, PubNub CTO Stephen Blum gives a quick overview and use case for HTTP long polling.
Full blog post and diagrams: pubnub.com/blog/http-long-polling/
Music: "4227" by Saoe (soundcloud.com/saoesound/4227a)