UTC

Coordinated Universal Time, the agreed-upon baseline for the world's timezones. The mismatched initialism avoids favouring any particular language.

It is technically a refinement of what remains widely known as GMT, Greenwich Mean Time, being the solar time at an observatory in Greenwich, England, which became prominent in the Age of Exploration. Abbreviated Z in the single-letter military time zone system, the corresponding name Zulu is widely used.

The technical differences between UTC, GMT and variants such as UT0 are meaningful to such fields as astronomy.