What is an Android PendingIntent?

A PendingIntent is a token that you give to a foreign application (e.g. NotificationManager, AlarmManager, Home Screen AppWidgetManager, or other 3rd party applications), which allows the foreign application to use your application's permissions to execute a predefined piece of code.

If you give the foreign application an Intent, it will execute your Intent with its own permissions. But if you give the foreign application a PendingIntent, that application will execute your Intent using your application's permission.

A Pending Intent is a token you give to some app to perform an action on your apps' behalf irrespective of whether your application process is alive or not.

I think the documentation is sufficiently detailed: Pending Intent docs.

Just think of use-cases for Pending Intents like (Broadcasting Intents, scheduling alarms) and the documentation will become clearer and meaningful.

Why PendingIntent is required ? I was thinking like

1. Why the receiving application itself cannot create the Intent or
2. Why we cannot use a simple Intent for the same purpose.

E.g.Intent bluetoothIntent= new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);

If I send bluetoothIntent to another application, which doesn't have permission android.permission.BLUETOOTH_ADMIN, that receiving application cannot enable Bluetooth with startActivity(bluetoothIntent).

The limitation is overcome using PendingIntent. With PendingIntent the receiving application, doesn't need to have android.permission.BLUETOOTH_ADMIN for enabling Bluetooth. Source.