A device used to amplify a Wi-Fi signal in a network is known as a Wi-Fi extender or repeater. These devices receive existing wireless signals and rebroadcast them, extending the coverage area of a wireless network. Wi-Fi extenders are particularly useful in large homes or commercial spaces where the main router's signal may not reach all areas effectively. By improving signal strength and connectivity in hard-to-reach places, they enhance overall user experience by providing reliable internet access throughout the space.