<virtualType name="Magento\Payment\Model\Config\Data"
             type="Magento\Framework\Config\Data">
    <arguments>
        <argument name="reader" xsi:type="object">
            Magento\Payment\Model\Config\Reader\Proxy
        </argument>
        <argument name="cacheId" xsi:type="string">
            payment_config
        </argument>
    </arguments>
</virtualType>

This is a virtual type configuration.

This configuration is for the base area. Base area configurations will apply to all the sub-applications.

This virtualType configuration tells the Object Manager when a user wants a virtual Magento\Payment\Model\Config\Data object that it should return a Magento\Framework\Config\Data object.

This configuration tells the Object Manager that when a user wants a Magento\Payment\Model\Config\Data object that the following arguments should be used in the foo object's constructor.

• $reader = new Magento\Payment\Model\Config\Reader\Proxy (...)
• $cacheId = "payment_config";