Global Navigation Satellite System
A system comprised of multiple satellites orbiting the earth, transmitting precise radio timing signals, and receiver devices on earth that use the signals to determine their precise location on the planet.
There are many types of receiver devices, but nearly all modern phones include a GNSS technology.
There are multiple GNSSs, created by different governments and organizations around the world. Each system has its own separate fleet of satellites, although many use nearly the same radio frequencies, making it easy for receiver devices to use multiple networks at the same time.
GPS is the GNSS created by the United States. GLONASS is the Russian system, and Galileo is run by the European Union.