International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time stanard that tracks proper time on Earth's geoid. It is the principal realisation of Terrestrial Time, and the basis for Coordinated Universal Time (UTC) which is used for civil timekeeping all over the Earth's surface. As of 2006 TAI is exactly 33 seconds ahead of UTC: 10 seconds' initial difference at the start of 1972, plus 23 leap seconds in UTC since 1972.