What is the difference between GPS and GNSS?

GPS is a satellite navigation system developed by the United States government for the US Department of Defense. It is the most commonly used navigation system in the world, and features 32 satellites across the globe. GLONASS is a satellite navigation system developed by the Russian Aerospace Defence Forces and has 29 total satellites orbiting Earth. GPS, GLONASS, and a handful of other navigation systems that are currently being developed, all fall under the GNSS umbrella. When using a GPS device, you are only accessing GPS satellites; when using a GNSS device, you are accessing satellites from multiple constellations  in orbit for greatly enhanced accuracy and reliability of information.