A "shaft" is a long, narrow, cylindrical part that can be found in various machines and tools. It often serves as a support or a means to transmit power or motion. For example, in a bicycle, the shaft connects the pedals to the gears, allowing the bike to move. In construction, a shaft can refer to a vertical passage, such as in a building for elevators or plumbing. These shafts are essential for the efficient movement of people and materials within a structure, ensuring that services like electricity and water can be delivered effectively.