An airbill is a waybill for cargo being shipped by air.
An airwaybill is another word for an airbill, a waybill for cargo being shipped by air.
You will use a Fedex USA Airbill, when you are shipping US to US Express Service Packages ONLY! International services you would use an international airway bill. Ground services you too will have a separate labels. Along with Freight, you use a different label.