Leonardo da Vinci's flapping-wing flying-machine design is an ornithopter.
An ornithopter is an aircraft intended to fly by flapping wings, imitating the motion of birds, bats, or insects. Leonardo studied bird flight extensively and filled notebooks with observations about wing movement, balance, air currents, and the role of the tail.
His proposed human-powered ornithopters generally used a pilot lying or standing inside a frame and operating wing mechanisms with hands and feet. The drawings show serious attempts to translate animal flight into mechanical motion, but human muscles cannot provide enough sustained power for a practical flapping aircraft of the proposed scale.
Leonardo also explored gliding and screw-based flight. His ornithopter studies therefore belong to a wider investigation of aviation rather than a single completed aircraft. Modern ornithopters exist as small experimental or model aircraft, but Leonardo's human-carrying versions were never demonstrated in flight.