A flywheel is a mechanical device that stores rotational energy. It consists of a heavy wheel that spins around an axis, and its inertia helps maintain a consistent speed. When energy is added, the flywheel accelerates, and when energy is needed, it releases that stored energy, providing a smooth and steady output. Flywheels are commonly used in various applications, including electric vehicles, energy storage systems, and industrial machinery. They help improve efficiency by balancing energy supply and demand, making them valuable in both renewable energy systems and traditional power generation.