On the App Store (iOS and AppleTV apps), you can add a subtitle. It can be used to provide a brief description of your app.
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The Subtitle field can be used complementary to the app's name.

Avoid using generic sentences like "the best app in the world." Instead, emphasize the distinctive features or common applications of your app that resonate with your target audience.

This is currently an iOS/tvOS-only field that will show up below your app's title in the App Store. This field has a 30-character limit, so keep it simple and to the point.

More details and Apple guidelines can be found at:
​https://developer.apple.com/app-store/product-page/
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​Example: