When the owner of male genitalia enters their parter while being completely hard, using their appendage as the only body part to which they prop their body upward in an open armed and legged position presenting that of a bird in flight - typically facing in opposite directions, thus the “reverse” description. The position was inspired by the old 90s toy of a plastic bird figure that balanced gracefully on the tip of a finger appearing to be in flight.
Luke preformed a reverse thunderbird on Phil after an exceptional band practice that left both aroused and ready to fly.