International Atomic Time (TAI) is a high-precision time standard that is based on the vibrations of atoms, specifically cesium atoms. It is defined by the International Bureau of Weights and Measures and is measured using atomic clocks, which are incredibly accurate and can keep time to within billionths of a second. TAI serves as the foundation for other time standards, including Coordinated Universal Time (UTC). While TAI is continuous and does not include leap seconds, UTC adjusts for Earth's irregular rotation by adding or subtracting these seconds, ensuring that civil time remains in sync with solar time.