UTC ? A global Timescale
Coordinated UNiversal Time - explained!
Atomic clocks use an atomic resonance frequency standard as their timekeeping element and are by far the most accurate chronometers possible with the latest Strontium based atomic clocks boasting a precision of a less than a second lost in several hundred million years.
The clocks maintain a continuous and stable time scale called International Atomic Time (TAI). However, for civil time, another time scale, Coordinated Universal Time (UTC)which is derived from TAI, but synchronized using leap seconds to UTC, to keep it based on the rotation of the Earth.