Google is enhancing the previously announced app content indexing in mobile search results. This feature was previously only available with a few apps and in limited regions, but now it's going worldwide (for English language content) and includes a bunch of new apps.
This is tied into Google Play app links in search, but it's a distinct feature. The idea here is that when you search for certain content, Google Search can check the web, but also what's listed inside apps. For example, if you search for a movie, Google might offer to open the IMDB app to the listing for that movie. Looking up a recipe? Google can queue up the matching entry in Allthecooks instantly. Google is essentially correlating a web link with a location inside an app.
Google already had support for deep links in apps like IMDB, Flixter, and Etsy, but now there are 24 new apps. Here's the list Google provided.
500px, AOL, BigOven, Bleacher Report, Booking.com, Eventbrite, Glassdoor, Goodreads, Huffington Post, Merriam-Webster, Pinterest, Realtor.com, Seeking Alpha, TalkAndroid, TheFreeDictionary, The Journal, TripAdvisor, Tumblr, Urbanspoon, Wattpad, Yellow Pages, Zagat, Zappos, and Zillow
Developers have to get on board with support for so-called "deep links," but the documentation is ready to guide them through the process. Those links are then shared with Google so they can be exposed in search results. You should start seeing a lot more of these links when performing mobile searches.