Global Navigation Satellite Systems (GNSS) are satellite-based systems that provide accurate location and time information anywhere on Earth. They work by using a network of satellites that transmit signals to receivers on the ground. By calculating the time it takes for these signals to reach the receiver, the system can determine the receiver's precise position. The most well-known GNSS is the Global Positioning System (GPS), developed by the United States. Other systems include GLONASS from Russia, Galileo from the European Union, and BeiDou from China. These systems are widely used in various applications, including navigation, mapping, and timing services.