Broadcast Reciever

Most of us are all too familiar with announcements in public places. They are loud messages that are meant to inform large groups of people about something important. Android applications also have to deal with announcements sometimes—announcements generated either by other applications or by the Android operating system itself. Such announcements are called broadcasts, and they are seen as an important form of asynchronous inter-process communication on the Android platform.

<receiver android:name="MyReceiver">
   
      <intent-filter>
         <action android:name="android.intent.action.BOOT_COMPLETED">
         </action>
      </intent-filter>
   
   </receiver>

https://code.tutsplus.com/tutorials/android-from-scratch-understanding-android-broadcasts--cms-27026