Coordinated universal time, UTC - standard time set on the basis of TAI (fr. Temps Atomique International), making allowance for the irregularity of the Earth’s rotational movement and coordinated in relation to solar time.

Coordinated Universal Time is expressed by means of 24-hours clock and uses the Gregorian calendar. It is used in aviation and sea navigation where it is known under its military name "Zulu time". (Zulu in the phonetic alphabet corresponds with the letter “z” which means the zero meridian, i.e. geographical longitude 0, in Greenwich, an English city).