Supplier is any company that supplies travel and/or related services to the traveling public
Other definition:
Supplier is actual producer of a unit of travel merchandise, such as a carrier, hotel or sightseeing operator.
Other definition:
Supplier is the those who supply travel trade with product. In the broadest sense, this could also include DMOs.
Other definition:
Supplier are those businesses that provide industry products like accommodations, transportation, car rentals, restaurants and attractions.