Instant run is a new feature introduced in Android Studio 2.0 that allows you to update your app while it is running on a device without building a new APK. This feature reduces deployment time.
Instant run requires SDK 15 or higher, though it's recommended to use SDK 21 or higher. You will also need to have your Android Plugin for Gradle updated to version 2.0 or higher. Instant run works for both the emulator and a real device.
After the first deployment of your app, you will note that the run/debug icon has changed and has an additional thunderbolt icon, such as the debug icon in the following screenshot:
The next time you click on the ...