About Android Application

An Android Application (App, is A single installable unit with can be started independently.
An Android application consists of configuration files and Java Source and resource files.

Application : 
An Android application has only one Application class which is initiated before any other android component, it is the last component with is stopped when application shutdown.
Activity : 
Activity is a visual representation of the application, An Android application have multiple activities.
Activities use views and fragments create their user interfaces and interact with user
Service: 
performs tasks without providing a user interface. They can communicate with other Android components and send notifications to the user. For example, a broadcast receiver can notify the user via the notification framework in Android.

Broadcast receiver (short: receiver):
A receiver can be registered to listen to system messages and intents. A receiver gets notified by the Android system if the specified event occurs.

For example, you can register a receiver for the event that the Android system finished the boot process. Or you can register for the event that the state of the phone changes, e.g., someone is calling.

Content provider (short: provider):
A provider defines a structured interface to application data. A provider can be used for accessing data within one application, but can also be used to share data with other applications.

Android contains an SQLite database which is frequently used in conjunction with a content provider. The SQLite database would store the data