App indexing allows apps to be discoverable through search engines like Google by deep linking relevant app content to webpages. It involves implementing deep links within mobile apps, using the App Indexing API for platforms like Android, and mapping webpages to corresponding app screens. Doing so provides opportunities to improve an app's visibility in search and can positively impact the ranking of associated websites. While technical implementation requires supporting HTTP URLs, adding API calls, and mapping links, app indexing's future benefits for discoverability are growing as apps become more integrated into search.