What term describes the feathers located on the lower part of a bird's wings that play a crucial role during flight?

The term that accurately describes the feathers located on the lower part of a bird's wings, which are crucial for flight, is secondary feathers. These feathers are attached to the ulna bone of the wing and contribute significantly to the overall wing structure and functionality. They provide lift and help with the maneuverability of the bird in flight.

Primary feathers, on the other hand, are found on the outer part of the wing and are primarily responsible for propulsion and thrust. Tertiary feathers are located closer to the bird's body and provide additional support but are not as critical during regular flight dynamics as the secondary feathers. Tail feathers, while important for stabilization and steering, do not play a direct role in the wing structure itself. Therefore, secondary feathers are the correct term for those located on the lower part of the wings essential for flight.