In traditional web development, there has not been a way to maintain a persistent connection between a client browser and the web server. Web developers have gone to great lengths to try and simulate a connected world in the request/response world of HTTP.
Several developers have met with success using creative thinking and loopholes within the standard itself to develop techniques such as long polling and the forever frame. Now, thanks to the realization that such a technique is needed, the organizations overseeing the next generation of web standards are also heeding the call with server-sent events and web sockets.
Long polling is the default fallback for any client and server content exchange. It is not reliant on anything but HTTP—no special standards checklists or other chicanery are required.
Long polling is like getting the silent treatment from your partner. You ask a question and you wait indefinitely for an answer. After some known period...