What is <fieldsets/ > stands for?

Question

When I have gone through Mage_Bundle module in magento, I found this code snippet inside app/code/core/Mage/Bundle/etc/config.xml.

<admin>
    <fieldsets>
        <catalog_product_dataflow>
            <is_in_stock>
                <product_type>
                    <bundle/>
                </product_type>
            </is_in_stock>
            <manage_stock>
                <product_type>
                    <bundle/>
                </product_type>
            </manage_stock>
        </catalog_product_dataflow>
    </fieldsets>
    ...
</admin>

What is this <fieldsets /> stands for ? I have searched a lot. But every reference is describing about system fieldsets. Can anyone here describe, what is this for ?

Thanks in advance.