App indexing refers to the indexing of content contained in mobile apps by search engines. App indexing has enabled search engines to provide search results from within apps in addition to those from mobile or desktop websites. If the content the user searched for exists on an app which is installed on the user's smartphone, Google will present a "deep link" leading to that content. If the user doesn't have the app, Google will offer an install card for the app in the search results.
How does app indexing work?
In 2013, Google announced it will be indexing content in apps. This means app content is now found in Google's index, helping apps and sites surface in Google mobile search through auto-complete. When a user searches for content that is already in the app, they will see the app directly in the search results. When a user searches for content contained in an app, and the app is installed in the user's device, the user will have an option to view the content within the app instead of on a mobile webpage.
Google indexes the content either through a sitemap file or through Google Search Console.
Why is app indexing important?
The average user has a number of apps on their phone that they simply don't use. In fact, the vast majority of those unused apps are only ever used once. Although this is bad for app creators, it can be solved with app indexing. By having an app in the Google index, if the user searches for content that is in the app, it will appear in search. Clicking on the app in search will result in the app being launched directly from Google search resulting in the user re-engaging with the app already on their phone.
What is the difference between app indexing and deep linking?
App indexing and deep linking have different goals. App indexing is designed to make an app searchable on Google. A deep link on the other hand is a URL that takes a user to a specific location on an app. The reason deep linking is necessary is that apps don't work the same way that a browser does. If a searcher wants to find a specific webpage, they can enter the URL into the browser. On the other hand, for the link to take the user to a specific place on the app, the app needs to be configured.