Notification channel
An Android category of notifications, such as Orders or Promotions, that users can turn on or off and configure in Settings.
Definition
Since Android 8, every notification must belong to a channel the app has created, or it isn't shown. The app sets the initial importance, sound and vibration; after that only the user can change them. Channels should match what users want to control separately. Android 13 also requires the POST_NOTIFICATIONS permission.
In practice
A shop creates "Order updates" at default importance and "Offers" at low importance.