Another application component can start a service, and it continues to run in the background even if the user switches to another application. Additionally, a component can bind to a service to interact with it. For example, a service can handle network transactions, play music, perform file I/O, or interact with a content provider, all from the background.
A notification is a message that Android displays outside your app’s UI to provide the user with reminders, communication from other people, or other timely information from your app. Users can tap the notification to open your app or take an action directly from the notification.