[astronomy]
The official timekeeping system of the world's nations since 1972. It refers local time throughout the world to time at the prime meridian. It is based on atomic clocks but is periodically artificially adjusted to always remain within 0.9 seconds of universal time. The adjustment is made by the addition of leap seconds to the course of atomic time. Coordinated universal time is also known as UTC. The acronym UTC does not represent the word order of coordinated universal time in either English or French—the official languages of the International Telecommunication Union (ITU). It is an extension of the UT* pattern established for versions of universal time.