What does "main screen" actually refer to, in battery usage? On iOS 8, there is the battery usage screen showing an estimate of the battery use, per application.

It also has an entry for "Main screen". I assumed it was just displaying the main screen with the icons, but I got 40% of that during night, during which the screen was indeed off.

As such, what does "Main screen" refer to, exactly?
From https://www.apple.com/batteries/maximizing-performance/#ios:


  Home &amp; Lock Screen. This indicates that the Home screen or Lock screen
  was displayed on your device. For example, the display was awakened by
  pressing the Home button or by a notification.
  
  
  If an app frequently wakes your display with notifications, you can turn off push notifications for the app in Settings > Notifications.
  Tap App and set Allow Notifications to Off.