A feature of the Android operating system starting with Android 5.0 that enables an app to be downloaded and run without being installed. Google Play Instant allows an app to run like a Web app activated within the browser. No software is installed and nothing is stored locally in the user's phone or tablet.
Instant apps are developed because they download and run very quickly like the code on a Web page. They are also created to entice users to download the full version, which has to be installed and reside within the user's device. Developers who want to create an instant app from their installable version can find the task easy or difficult depending on how the original code was architected. See Android
and Google Play