What is "Use APK Expansion Files"feature for Android?

Google Play currently requires an APK file be no more than 100MB hence to enable user to create an app above 100 MB "Use APK Expansion Files" option is introduced. This will create one more file in "Download" with extension .obb (.obb file needs to be upload along with .apk while uploading .apk file on Google Play Store via Google Developer Console).

Location : Package >> Platform >> Split Package for more than 100MB >> Use APK Expansion Files