A "pinion" is a type of gear with a small number of teeth, designed to mesh with a larger gear, known as a crown gear. It is commonly used in various mechanical systems to transmit motion and force. The pinion's rotation drives the larger gear, allowing for changes in speed and torque. In addition to its mechanical use, the term "pinion" can also refer to a specific type of bird, particularly the feathers on the wing that are crucial for flight. These feathers help provide lift and control, making them essential for the bird's ability to navigate through the air.