The Google Search app is already the quickest way to retrieve information on your Android device. With just a few words, users can search the web, open apps, and pull up directions. The problem is that some information opens up in a web browser that would be better suited for an app. If you already have the IMDb app installed, why should a search result shoot you out to the browser? Some links ask which app you want them to open in, but how can you tell which ones?
With app indexing, users will soon have more control over the experience. An Open in app button, referred to as a "deep link," will appear next to links that are capable of opening content within an app that's already been installed on your device.
The goal is for users to have a more seamless search experience, and with any luck, this will further remove the need to fall back to the app drawer. Developers looking to get a better understanding of this new functionality can pull more information from the DevBytes video below.
Google is currently testing app indexing with an initial group of developers that includes Etsy, Expedia, Flixster, IMDb, Newegg, OpenTable, Wikipedia, and several others. US Android users can expect to see deep links appear for these apps in the coming weeks.
Source: Android Developers Blog