UTC

UTC, or Coordinated Universal Time, is the primary time standard by which the world regulates clocks and time. It is a successor to Greenwich Mean Time (GMT) and is used for civil timekeeping, navigation, and the time standards used in computing and telecommunications. UTC is based on International Atomic Time (TAI), a continuous time scale generated by highly accurate atomic clocks. To keep UTC in line with the Earth's irregular rotation, leap seconds are inserted (or occasionally removed) as needed by the International Earth Rotation and Reference Systems Service (IERS). The result is a timescale that remains within about one second of UT1, a time scale that tracks mean solar time.

TAI and UTC differ by a fixed integer number of seconds; the offset changes when leap seconds are added. The maintenance of UTC is a collaborative effort coordinated by the Bureau International des Poids et Mesures (BIPM) in conjunction with IERS and national metrology institutes.

In practical use, UTC serves as the basis for civil time and for time zones worldwide. It underpins ISO 8601 date and time representations and is the reference for computer clocks, telecommunications, aviation, finance, and weather services. When time zones are expressed with a "+/- offset" from UTC (for example, UTC+02:00), they describe local civil time relative to UTC.

Leap seconds are announced by the IERS typically several months in advance; there is ongoing debate about whether to abolish or reform leap seconds in the future. For most users, UTC provides a stable, globally synchronized reference for timekeeping.