"As a best practice in my development of Android apps in the past, activities are really the complete screen that a user experiences as part of the app. Fragments are really small sub-activities that take place within the activity. Because fragments within an app have their own life cycle and receive their own input events within the app, there are specific times when fragments make the most sense in development. In my experience, I always use fragments when the app is working with UI components that will be used across multiple activities within the app. As well, fragments have also served very well when using swipe views within the app."
