Google does a sterling job of indexing web sites, but many users now rely on mobile apps to browse content. Google now wants to index the content of those apps as well. Here's how it will work.
Google has commenced a limited trial of indexing app content with a select group of developers. For those apps, once deep linking into the app is enabled and the sitemap for its associated site is updated, search results which include relevant content for an app installed on the user's phone will offer the option of opening the result directly in the app. Hence if you were searching for a product and found a relevant result on eBay, it could launch the installed eBay Android app rather than a browser page.
The initial trial is US-only, but we'd expect Google to expand if it proves successful. The lines for search are increasingly blurring; Windows 8.1, for instance, shows search results from Bing as well as the user's local system, though it doesn't yet trigger in-app links.
Indexing apps just like websites [Google Webmaster Central]