long-polling

 Long-polling  is a common technique to create a push-like experience through polling by having the poll request wait for an item when there are none ready, rather than return an empty response.

Uses

 * On the client-side long-polling has been a common technique to implement realtime experiences. It has now started to be superseded by eventsource, websockets and web push notifications as supported by Firefox and Chrome. Long-polling can also be used to polyfill eventsource.
 * Amazon SQS has support for long-polling to reduce the number of requests needed when the queue is empty.