Definition of 

App referrer

What's 
App referrer
: it is one of the possible values for
Source Type
. It means:
Users who discovered your app from within another app. Includes impressions and page views loaded in a store sheet. Includes Apple apps, such as Messages, except Safari.

See other fields from

Analytics: Discovery and Engagement

Explore more Reports from

App Store Connect

The (only) data hub made for apps