BroadcastReceiver (receiver) is an Android component which allows you to register for system or application events. All registered receivers for an event are notified by the Android runtime once this event happens.
for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured.
Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use.