Leonardo da Vinci's bird-inspired flying-machine concept was an ornithopter.
An ornithopter is an aircraft intended to fly by flapping wings, rather than by using fixed wings or a powered rotor. Leonardo studied birds and bats and made numerous sketches of wing structures, harnesses, and mechanical linkages that could transmit a person's movement to wings.
His designs show careful attention to anatomy and aerodynamics, but they were not proven working aircraft. Human muscles cannot provide enough sustained power for a machine of the size he imagined, a limitation that later designers also encountered.
The word ornithopter comes from Greek roots meaning bird and wing. Modern ornithopters, including small robotic models, can flap successfully, but Leonardo's proposed human-powered machines remained experimental designs.