One of the biggest new features found in iOS 9 is the adoption of universal search. Universal search is a new feature that allows you to search for content within apps directly from Spotlight search.
On previous versions of iOS, searching was limited to the web and first party Apple apps pre-installed on iOS. For example, with older version of iOS you could search for contents within the Notes app, but couldn't do so for third-party note apps.
With iOS 9's new Spotlight search abilities, you can now search and discover content buried deep within the apps on your iPhone. It makes Spotlight feel truly useful and brand new.