In an effort to help people start using apps faster, Google has introduced Android Instant Apps. These apps startup instantly, without the need to actually install themselves onto your device, instead running from the cloud, just like tapping a link to load a webpage.
Apps are split into modules, allowing Google Play to download only the parts that are necessary at a given time. With a couple of taps, you can install the rest of the app while you use the parts you need at the moment. With Instant Apps you can, for example, tap on a link for a product on an online store, which will then take you to that products page in the store's app without installing the app first.
Developers can update existing apps, modularizing them for Google Play to take advantage of this feature, and users will be more readily able to find your apps in more ways, not just through Google Play. Instant Apps will also be backward compatible with devices running Android 4.1 Jelly Bean.
Google notes that Instant Apps won't be prevalent for some time. For the moment, it is working with a small group of developers on the feature, which will roll out to more developers over time. Users should start seeing Instant Apps later this year.