In 1983, the standard meter was redefined by international agreement as the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second. This redefinition effectively fixed the speed of light in vacuum at exactly 299,792,458 meters per second, making the meter dependent on a fundamental physical constant rather than a physical object or a specific wavelength of light

. Previously, the meter had been defined by physical artifacts (such as the platinum-iridium meter bar) or by the wavelength of light emitted by krypton-86 atoms. The 1983 definition replaced these with a definition based on the invariant speed of light, which is a universal constant. This change allowed for a more precise, stable, and universally accessible standard of length. The redefinition did not significantly change the actual length of the meter but improved the precision and reproducibility of the unit. The goal was to maintain continuity with previous definitions while providing a more fundamental and reliable basis for the unit of length

. Summary:

• Redefined in 1983 as the distance light travels in vacuum in 1/299,792,458 of a second.
• Fixed the speed of light at exactly 299,792,458 m/s.
• Replaced physical artifact and wavelength-based definitions.
• Improved precision and universality without changing the meter's length significantly