<type name="Magento\Shipping\Model\Carrier\AbstractCarrier">
    <arguments>
        <argument name="logger" xsi:type="object">
            Magento\Shipping\Model\Method\VirtualLogger
        </argument>
    </arguments>
</type>

This is a type configuration.

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

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

• $logger = new Magento\Shipping\Model\Method\VirtualLogger (...)

<virtualType name="Magento\Shipping\Model\Method\VirtualLogger"
             type="Magento\Framework\Logger\Monolog">
    <arguments>
        <argument name="handlers" xsi:type="array">
            <item name="debug" xsi:type="object">
                Magento\Shipping\Model\Carrier\VirtualDebug
            </item>
        </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\Shipping\Model\Method\VirtualLogger object that it should return a Magento\Framework\Logger\Monolog object.

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

• $handlers = [...items...];