The description list is used for to identify the type of private fare being purchased.

NAME	DESCRIPTION	FORMAT	ALLOWED/POSSIBLE VALUES	NDC SERVICES
<DataLists / DescriptionList>
Description Attribute ObjectKey	Type of private fare	Alphabetical	Requested product in AirShopping	AirshoppingRS OrderViewRS OfferPriceRS OrderReshopRS
Description / Text	Description of private fare	Alphabetical	Requested product in AirShopping	AirshoppingRS OrderViewRS OfferPriceRS OrderReshopRS

DescriptionList example

<DescriptionList>
	<Description ObjectKey="TO">
		<Text>TO</Text>
	</Description>
</DescriptionList>

IB NDC Documentation