<virtualType name="shellBackground" type="Magento\Framework\Shell">
    <arguments>
        <argument name="commandRenderer" xsi:type="object">
            Magento\Framework\Shell\CommandRendererBackground
        </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 shellBackground object that it should return a Magento\Framework\Shell object.

This configuration tells the Object Manager that when a user wants a shellBackground object that the following arguments should be used in the foo object's constructor.

• $commandRenderer = new Magento\Framework\Shell\CommandRendererBackground (...)