(a)The term “stockyard owner” means any person engaged in the business of conducting or operating a stockyard;
(b)The term “stockyard services” means services or facilities furnished at a stockyard in connection with the receiving, buying, or selling on a commission basis or otherwise, marketing, feeding, watering, holding, delivery, shipment, weighing, or handling in commerce, or livestock;
(c)The term “market agency” means any person engaged in the business of
(1) buying or selling in commerce livestock on a commission basis or
(2) furnishing stockyard services; and
(d)The term “dealer” means any person, not a market agency, engaged in the business of buying or selling in commerce livestock, either on his own account or as the employee or agent of the vendor or purchaser.