A tuned mass damper is a device used to reduce vibrations in structures, such as buildings and bridges. It consists of a large mass that is mounted on springs and dampers, allowing it to move independently of the structure. When the building sways due to wind or seismic activity, the mass moves in the opposite direction, helping to stabilize the structure. These devices are commonly found in tall buildings, like the Taipei 101, where they help prevent excessive movement during strong winds or earthquakes. By absorbing and dissipating energy, tuned mass dampers enhance the safety and comfort of occupants in these structures.