https://en.wikipedia.org/wiki/Push_technology#Long_pollingWith long polling, the client requests information from the server exactly as in normal polling, but with the expectation the server may not respond immediately. If the server has no new information for the client when the poll is received, instead of sending an empty response, the server holds the request open and waits for response information to become available. Once it does have new information, the server immediately sends an HTTP/S response to the client, completing the open HTTP/S Request.