The coolest iOS 9 feature you probably don't know about

There are a lot of changes in iOS 9, Apple's big software update for the iPad, iPhone, and iPod touch, released this week.

In addition to making improvements to Siri and battery life, Apple has also upgraded how you can interact with third-party apps. Apple now supports what it calls "deep linking" apps. Deep linking essentially allows apps to talk to one another, as well as to the rest of iOS, in ways previously not possible.

Deep linking sounds nerdy at first, but once all of your favorite apps support it, the feature has the potential to speed up how you move between apps and make you more productive.

There are two kinds of deep linking that apps can do in iOS 9 - they can link to each other, and they can link to your search results in Spotlight.

When apps link to each other, it looks something like this: you click on a link to a pair of shoes on Amazon from your Twitter feed. Normally, the link would open in Safari. But with deep linking in iOS 9 and the official Amazon app installed on your phone, tapping the link in Twitter could bypass Safari and take you directly to Amazon's app.

This kind of linking between apps makes even more sense for apps like Yelp and Foursquare, which offer more functionality (like the ability to rate a restaurant) through their iPhone apps than their websites.

Another way deep linking could work: If someone shares a song on Facebook from Spotify, clicking on it could open the Spotify app on your phone instead of taking you to Spotify's mobile website.

In Spotlight, apps can also use deep linking to surface content directly in search results. This was previously limited to select few, Apple-approved sources, like Bing search results and Wikipedia. Now any app that supports deep linking in iOS 9 can show up in search.

Slack and Pocket have already updated their apps with deep linking for iOS 9 and are both great examples. I use Slack to communicate with the rest of the Tech Insider team, and now I can search for my editor and open our Slack conversation directly from Spotlight.

With Pocket, a service I use to bookmark articles from the web that I want to read later, I can search for content I have saved to read without opening the app itself.

The usefulness of deep linking is going to depend entirely on whether or not developers chose to support it in their apps - many already have - and if people know the functionality exists in the new mobile operating system.

Once you know about deep linking, it could change the way you use your iPhone.