Manifest targeting allows developers to set rules and requirements for their applications while ensuring maximum compatibility among customers downloading apps from the Amazon Appstore. These are device-specific requirements included in the AndroidManifest.xml that allows for any devices failing to meet the specified criteria to be filtered out.
An application could require the use of a device's camera to take photos, or gyroscope to detect the device’s orientation. With manifest targeting these features can be explicitly called out as a requirement. Any device lacking these will show up as not supported. There are dozens of possible rules, from setting minimum screen sizes to requiring specific versions of Android. For more technical details regarding manifest targeting see the following documentation:
Introduction to Device Targeting: https://developer.amazon.com/public/support/submitting-your-app/tech-docs/getting-started-with-device-targeting
Supported Filters on the Amazon Appstore: https://developer.amazon.com/public/support/submitting-your-app/tech-docs/supported-filters-on-the-amazon-appstore
(for setting version requirements): http://developer.android.com/guide/topics/manifest/uses-sdk-element.html