| Coordinated Universal Time (UTC) | The world’s time standard; a coordinated time scale maintained by the Bureau International des Poids et Mesures (BIPM) based on solar time (measured by the Earth’s rotation) and closely synchronized time scales derived from hundreds of highly precise atomic clocks around the globe (e.g., UTC(NIST), UTC(USNO)) [info] |
| Critical Infrastructure | The assets, systems, and networks that provide functions necessary for the safe operation of a nation (or the world) [info] |
| EO 13905 | Executive Order 13905 entitled “Strengthening National Resilience through Responsible Use of Positioning, Navigation, and Timing Service” [info] |
| Global Navigation Satellite Systems (GNSS) | The general class of satellite constellations providing signals from space that transmit PNT information globally; currently GPS (United States), Galileo (European Union), GLONASS (Russia), and BeiDou (China) |
| Global Positioning System (GPS) | A U.S.-owned utility that provides users with PNT services [info] |
| Low Earth Orbit (LEO) | An Earth-centered orbit with an altitude of 2,000 km (1,200 miles) or less |
| Navigation | A service or facility that provides a source of information about where a person or thing is moving |
| Open PNT Industry Alliance | A coalition of manufacturers and service providers that have dedicated themselves to helping their customers back up GPS/GNSS by delivering alternative forms of PNT [info] |
| PNT | Acronym for Positioning, Navigation, and Timing |
| Positioning | A service or facility that provides a source of information about the current location of a person or thing |
| Satellite Time and Location (STL) | Commercial PNT service from Satelles that is a source of time [info] |
| Timing | A service or facility that provides a source of precise time to a person or thing |
| Timing Synchronization | The process of or an application for aligning the time between two or more systems |
| UTC(NIST) | U.S. time scale managed by the National Institute of Standards and Technology [info] |
| UTC(USNO) | U.S. time scale managed by the U.S. Naval Observatory [info] |