A bird's "train" refers to its:

The term "train" in the context of bird anatomy specifically refers to the long feathers found at the back of a bird, which are part of its tail. These feathers can serve several purposes, including aiding in flight, providing balance, and playing a role in mating displays. The train is most prominently observed in certain species of birds, such as peacocks, where the tail feathers can be elongated and colorful, enhancing their attractiveness during courtship. Understanding this terminology is essential for falconers, as it helps identify and describe different aspects of the birds they might train and hunt with.