<type name="Magento\Framework\App\FrontController">
    <plugin name="requestPreprocessor"
            type="Magento\Store\App\FrontController\Plugin\RequestPreprocessor"
            sortOrder="50"></plugin>
</type>

This is a type configuration.

This configuration is for the frontend area. This is the area that corresponds with the cart sub-application.

This configuration also tells the object manager to use the Magento\Store\App\FrontController\Plugin\RequestPreprocessor plugin class with Magento\Framework\App\FrontController objects.